diff --git a/core/base/inc/Byteswap.h b/core/base/inc/Byteswap.h
index b533bcbd80132..6a674861b842e 100644
--- a/core/base/inc/Byteswap.h
+++ b/core/base/inc/Byteswap.h
@@ -47,7 +47,7 @@
 #endif
 
 #if defined(_WIN32) && (_MSC_VER >= 1300)
-# include <stdlib.h>
+# include <cstdlib>
 # pragma intrinsic(_byteswap_ushort,_byteswap_ulong,_byteswap_uint64)
 # define R__USEASMSWAP
 #endif
diff --git a/core/base/inc/Strlen.h b/core/base/inc/Strlen.h
index 355780fabc441..7f1cb19a56549 100644
--- a/core/base/inc/Strlen.h
+++ b/core/base/inc/Strlen.h
@@ -14,7 +14,7 @@
 #include <ROOT/RConfig.hxx>
 
 #ifdef NEED_STRING
-#include <string.h>
+#include <cstring>
 #endif
 
 #endif
diff --git a/core/base/inc/TException.h b/core/base/inc/TException.h
index 5e28906b64e9a..ba8e87cbe2469 100644
--- a/core/base/inc/TException.h
+++ b/core/base/inc/TException.h
@@ -22,7 +22,7 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include <setjmp.h>
+#include <csetjmp>
 
 #include <ROOT/RConfig.hxx>
 #include "DllImport.h"
diff --git a/core/base/inc/TObject.h b/core/base/inc/TObject.h
index c81a3a0944fef..5456204156b2d 100644
--- a/core/base/inc/TObject.h
+++ b/core/base/inc/TObject.h
@@ -18,7 +18,7 @@
 #include "TStorage.h"
 #include "TVersionCheck.h"
 
-#include <stdarg.h>
+#include <cstdarg>
 #include <string>
 #include <iosfwd>
 
diff --git a/core/base/inc/Varargs.h b/core/base/inc/Varargs.h
index 878c9801f857e..2abae14d4837e 100644
--- a/core/base/inc/Varargs.h
+++ b/core/base/inc/Varargs.h
@@ -20,7 +20,7 @@
 #   define va_arg(ap, mode) ((mode*) __builtin_va_arg_incr((mode*)ap))[0]
 #   define va_(arg) __builtin_va_alist
 
-#   include <stdio.h>
+#   include <cstdio>
 
    extern "C" {
       int vfprintf(FILE*, const char *fmt, va_list ap);
@@ -28,7 +28,7 @@
    };
 
 #else
-#   include <stdarg.h>
+#   include <cstdarg>
 #   if defined(sparc) && !defined(__GNUG__) && !defined(__CC_SUN21__) && !defined(__SVR4)
 #      define va_(arg) __builtin_va_alist
 #   else
diff --git a/core/base/src/Match.cxx b/core/base/src/Match.cxx
index 919c86e30e924..da5226cb608a5 100644
--- a/core/base/src/Match.cxx
+++ b/core/base/src/Match.cxx
@@ -18,9 +18,9 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include <stdio.h>
-#include <ctype.h>
-#include <string.h>
+#include <cstdio>
+#include <cctype>
+#include <cstring>
 
 
 #include "Match.h"
diff --git a/core/base/src/TDatime.cxx b/core/base/src/TDatime.cxx
index e4a96c31c42f2..fbc5fc17a568d 100644
--- a/core/base/src/TDatime.cxx
+++ b/core/base/src/TDatime.cxx
@@ -30,7 +30,7 @@ required, use TTimeStamp.
 
 #ifdef WIN32
 #include "Windows4Root.h"
-#include <string.h>
+#include <cstring>
 #endif
 
 #include "TBuffer.h"
diff --git a/core/base/src/TMD5.cxx b/core/base/src/TMD5.cxx
index acad811fe519c..bc62fca63f452 100644
--- a/core/base/src/TMD5.cxx
+++ b/core/base/src/TMD5.cxx
@@ -33,8 +33,8 @@ array with the  digest.
 #include "TError.h"
 #include "TSystem.h"
 #include "Bytes.h"
-#include <string.h>
-#include <errno.h>
+#include <cstring>
+#include <cerrno>
 #ifdef R__WIN32
 #include <io.h>
 #endif
diff --git a/core/base/src/TMathBase.cxx b/core/base/src/TMathBase.cxx
index 93e3cafe44480..f851291770578 100644
--- a/core/base/src/TMathBase.cxx
+++ b/core/base/src/TMathBase.cxx
@@ -21,7 +21,7 @@ a stable file and used in place of TMath.h in the ROOT miniCore.
 */
 
 #include "TMathBase.h"
-#include <math.h>
+#include <cmath>
 
 ////////////////////////////////////////////////////////////////////////////////
 /// Return next prime number after x, unless x is a prime in which case
diff --git a/core/base/src/TStorage.cxx b/core/base/src/TStorage.cxx
index ba45033a24733..7573bd0828fa2 100644
--- a/core/base/src/TStorage.cxx
+++ b/core/base/src/TStorage.cxx
@@ -30,7 +30,7 @@ Set the compile option R__NOSTATS to de-activate all memory checking
 and statistics gathering in the system.
 */
 
-#include <stdlib.h>
+#include <cstdlib>
 
 #include "TROOT.h"
 #include "TObjectTable.h"
diff --git a/core/base/src/TString.cxx b/core/base/src/TString.cxx
index 3861da1022082..97695942bf2ea 100644
--- a/core/base/src/TString.cxx
+++ b/core/base/src/TString.cxx
@@ -44,8 +44,8 @@ as a TString, construct a TString from it, eg:
 */
 
 #include <ROOT/RConfig.hxx>
-#include <stdlib.h>
-#include <ctype.h>
+#include <cstdlib>
+#include <cctype>
 #include <list>
 #include <algorithm>
 
@@ -714,13 +714,13 @@ UInt_t TString::Hash(ECaseCompare cmp) const
    typedef unsigned __int64 uint64_t;
 #else // defined(_MSC_VER)
    // Other compilers
-#include <stdint.h>
+#include <cstdint>
 #endif // !defined(_MSC_VER)
 
    // From MurmurHash.cpp:
 #if defined(_MSC_VER)
    // Microsoft Visual Studio
-#include <stdlib.h>
+#include <cstdlib>
 #define ROTL64(x,y)     _rotl64(x,y)
 #define BIG_CONSTANT(x) (x)
 #else   // defined(_MSC_VER)
diff --git a/core/base/src/TUUID.cxx b/core/base/src/TUUID.cxx
index df88ef7538dd2..b66e1c84d7eec 100644
--- a/core/base/src/TUUID.cxx
+++ b/core/base/src/TUUID.cxx
@@ -124,8 +124,8 @@ system clock catches up.
 #include "Bytes.h"
 #include "TVirtualMutex.h"
 #include "ThreadLocalStorage.h"
-#include <string.h>
-#include <stdlib.h>
+#include <cstring>
+#include <cstdlib>
 #ifdef R__WIN32
 #include "Windows4Root.h"
 #include <Iphlpapi.h>
diff --git a/core/base/src/TUri.cxx b/core/base/src/TUri.cxx
index f31e918818bab..c09bee98f3667 100644
--- a/core/base/src/TUri.cxx
+++ b/core/base/src/TUri.cxx
@@ -19,7 +19,7 @@ the different parts of an URI. The functionality is that of
 a validating parser.
 */
 
-#include <ctype.h>    // for tolower()
+#include <cctype>    // for tolower()
 #include "TUri.h"
 #include "TObjArray.h"
 #include "TObjString.h"
diff --git a/core/base/src/TUrl.cxx b/core/base/src/TUrl.cxx
index 0de3ddc3c02c0..e469458d12101 100644
--- a/core/base/src/TUrl.cxx
+++ b/core/base/src/TUrl.cxx
@@ -20,7 +20,7 @@ an URL. The supported url format is:
 ~~~
 */
 
-#include <stdlib.h>
+#include <cstdlib>
 #include "TUrl.h"
 #include "THashList.h"
 #include "TObjArray.h"
diff --git a/core/clingutils/src/RStl.cxx b/core/clingutils/src/RStl.cxx
index cd05c0e4d3a01..b14fe3f0ac440 100644
--- a/core/clingutils/src/RStl.cxx
+++ b/core/clingutils/src/RStl.cxx
@@ -17,7 +17,7 @@
 #include "TClingUtils.h"
 using namespace TClassEdit;
 
-#include <stdio.h>
+#include <cstdio>
 
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclTemplate.h"
diff --git a/core/cont/inc/TBits.h b/core/cont/inc/TBits.h
index 771c4bf2a1547..bac63d09d91c9 100644
--- a/core/cont/inc/TBits.h
+++ b/core/cont/inc/TBits.h
@@ -21,7 +21,7 @@
 //////////////////////////////////////////////////////////////////////////
 
 #include "TObject.h"
-#include <string.h>
+#include <cstring>
 
 class TBits : public TObject {
 
diff --git a/core/cont/src/TBtree.cxx b/core/cont/src/TBtree.cxx
index d7ce1827204b7..020a3b3e89084 100644
--- a/core/cont/src/TBtree.cxx
+++ b/core/cont/src/TBtree.cxx
@@ -169,7 +169,7 @@ item's own key).
 #include "TBuffer.h"
 #include "TObject.h"
 
-#include <stdlib.h>
+#include <cstdlib>
 
 
 ClassImp(TBtree);
diff --git a/core/cont/src/TExMap.cxx b/core/cont/src/TExMap.cxx
index c6c5b8abd6292..5146246067e30 100644
--- a/core/cont/src/TExMap.cxx
+++ b/core/cont/src/TExMap.cxx
@@ -21,7 +21,7 @@ method (linear probing).
 #include "TBuffer.h"
 #include "TError.h"
 #include "TMathBase.h"
-#include <string.h>
+#include <cstring>
 
 
 ClassImp(TExMap);
diff --git a/core/cont/src/TObjArray.cxx b/core/cont/src/TObjArray.cxx
index 711e0f5cdbc43..353dabaa31049 100644
--- a/core/cont/src/TObjArray.cxx
+++ b/core/cont/src/TObjArray.cxx
@@ -52,7 +52,7 @@ set to the owner of its own content.
 #include "TROOT.h"
 #include "TBuffer.h"
 #include "TVirtualMutex.h"
-#include <stdlib.h>
+#include <cstdlib>
 
 ClassImp(TObjArray);
 
diff --git a/core/dictgen/res/OptionParser.h b/core/dictgen/res/OptionParser.h
index 15c0c5d687345..6edd0db1a8e23 100644
--- a/core/dictgen/res/OptionParser.h
+++ b/core/dictgen/res/OptionParser.h
@@ -51,8 +51,8 @@ Bugs Fixed 8-7-12:
  */
 
 
-#include <stdio.h>
-#include <stdlib.h>
+#include <cstdio>
+#include <cstdlib>
 
 /**
  * @file
diff --git a/core/dictgen/res/cygpath.h b/core/dictgen/res/cygpath.h
index 6a200dd392ec5..01cb679af37c3 100644
--- a/core/dictgen/res/cygpath.h
+++ b/core/dictgen/res/cygpath.h
@@ -9,8 +9,8 @@
  *************************************************************************/
 
 #ifndef ROOT_CygPath
-#include <stdio.h>
-#include <stdlib.h>
+#include <cstdio>
+#include <cstdlib>
 #include <direct.h>
 #include <string>
 
diff --git a/core/dictgen/src/BaseSelectionRule.cxx b/core/dictgen/src/BaseSelectionRule.cxx
index 9f3ad3a27ca9e..6ded3443d5598 100644
--- a/core/dictgen/src/BaseSelectionRule.cxx
+++ b/core/dictgen/src/BaseSelectionRule.cxx
@@ -24,7 +24,7 @@
 #include "TClingUtils.h"
 
 #include <iostream>
-#include <string.h>
+#include <cstring>
 #include <cctype>
 
 #include "clang/Basic/SourceLocation.h"
diff --git a/core/dictgen/src/rootcling_impl.cxx b/core/dictgen/src/rootcling_impl.cxx
index e6d20854e92e6..35fb754a32be5 100644
--- a/core/dictgen/src/rootcling_impl.cxx
+++ b/core/dictgen/src/rootcling_impl.cxx
@@ -24,7 +24,7 @@
 #include <algorithm>
 #include <cstdio>
 
-#include <errno.h>
+#include <cerrno>
 #include <string>
 #include <list>
 #include <sstream>
@@ -64,7 +64,7 @@
 #endif // R__FBSD
 
 #if !defined(R__WIN32)
-#include <limits.h>
+#include <climits>
 #include <unistd.h>
 #endif
 
@@ -4463,7 +4463,7 @@ int RootClingMain(int argc,
 
    if (!isGenreflex) { // rootcling
       // ROOTCINT uses to define a few header implicitly, we need to do it explicitly.
-      if (interp.declare("#include <assert.h>\n"
+      if (interp.declare("#include <cassert>\n"
                          "#include \"Rtypes.h\"\n"
                          "#include \"TObject.h\"") != cling::Interpreter::kSuccess
          ) {
diff --git a/core/foundation/inc/ROOT/RConfig.hxx b/core/foundation/inc/ROOT/RConfig.hxx
index 5d45aebd656c5..fe8ba30f96931 100644
--- a/core/foundation/inc/ROOT/RConfig.hxx
+++ b/core/foundation/inc/ROOT/RConfig.hxx
@@ -104,7 +104,7 @@
 #      endif
 #   else
 #      define R__SUN
-#      include <stdlib.h>
+#      include <cstdlib>
 #   endif
 #   define R__UNIX
 #   define NEED_STRING
diff --git a/core/foundation/inc/TClassEdit.h b/core/foundation/inc/TClassEdit.h
index 19f44aacb13ab..ee69d729cf7fa 100644
--- a/core/foundation/inc/TClassEdit.h
+++ b/core/foundation/inc/TClassEdit.h
@@ -15,7 +15,7 @@
 
 #include <ROOT/RConfig.hxx>
 #include "RConfigure.h"
-#include <stdlib.h>
+#include <cstdlib>
 #include <stdexcept>
 #ifdef R__WIN32
 #ifndef UNDNAME_COMPLETE
diff --git a/core/foundation/inc/ThreadLocalStorage.h b/core/foundation/inc/ThreadLocalStorage.h
index 9e82d9d498ca6..69140c6a3c77a 100644
--- a/core/foundation/inc/ThreadLocalStorage.h
+++ b/core/foundation/inc/ThreadLocalStorage.h
@@ -182,8 +182,11 @@ T &TTHREAD_TLS_INIT(ArgType arg) {
 #  define TTHREAD_TLS_FREE(name)
 
 #elif defined(R__HAS_PTHREAD)
-
+#ifdef __cplusplus
+#include <cassert>
+#else
 #include <assert.h>
+#endif
 #include <pthread.h>
 
 #  define TTHREAD_TLS_DECLARE(type,name)                                     \
diff --git a/core/foundation/res/ROOT/RSha256.hxx b/core/foundation/res/ROOT/RSha256.hxx
index ab630b314b6f6..e2c84a8ab2a7d 100644
--- a/core/foundation/res/ROOT/RSha256.hxx
+++ b/core/foundation/res/ROOT/RSha256.hxx
@@ -15,8 +15,8 @@
 #include "Rtypes.h"
 
 #include <iostream>
-#include <stdlib.h>
-#include <stdint.h>
+#include <cstdlib>
+#include <cstdint>
 
 
 namespace ROOT {
diff --git a/core/meta/src/TBaseClass.cxx b/core/meta/src/TBaseClass.cxx
index fdffc4ac763d3..6198c874061f3 100644
--- a/core/meta/src/TBaseClass.cxx
+++ b/core/meta/src/TBaseClass.cxx
@@ -13,7 +13,7 @@
 #include "TBuffer.h"
 #include "TClass.h"
 #include "TInterpreter.h"
-#include <limits.h>
+#include <climits>
 
 #include "TVirtualMutex.h" // For R__LOCKGUARD
 
diff --git a/core/metacling/src/TCling.cxx b/core/metacling/src/TCling.cxx
index b654ee0b39112..b68db53a8a549 100644
--- a/core/metacling/src/TCling.cxx
+++ b/core/metacling/src/TCling.cxx
@@ -135,7 +135,7 @@ clang/LLVM technology.
 #include <map>
 #include <set>
 #include <stdexcept>
-#include <stdint.h>
+#include <cstdint>
 #include <fstream>
 #include <sstream>
 #include <string>
@@ -153,8 +153,8 @@ clang/LLVM technology.
 #define R__DLLEXPORT __attribute__ ((visibility ("default")))
 #include <sys/stat.h>
 #endif
-#include <limits.h>
-#include <stdio.h>
+#include <climits>
+#include <cstdio>
 
 #ifdef __APPLE__
 #include <dlfcn.h>
diff --git a/core/multiproc/src/TMPClient.cxx b/core/multiproc/src/TMPClient.cxx
index a7059b3af329a..73ca667647d0c 100644
--- a/core/multiproc/src/TMPClient.cxx
+++ b/core/multiproc/src/TMPClient.cxx
@@ -18,7 +18,7 @@
 #include "TSocket.h"
 #include "TSystem.h" //gSystem
 #include "TVirtualX.h" //gVirtualX
-#include <errno.h> //errno, used by socketpair
+#include <cerrno> //errno, used by socketpair
 #include <memory> //unique_ptr
 #include <sys/socket.h> //socketpair
 #include <sys/wait.h> // waitpid
diff --git a/core/newdelete/src/NewDelete.cxx b/core/newdelete/src/NewDelete.cxx
index 466f70a01758e..dcd4a947b53de 100644
--- a/core/newdelete/src/NewDelete.cxx
+++ b/core/newdelete/src/NewDelete.cxx
@@ -57,8 +57,8 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include <stdlib.h>
-#include <errno.h>
+#include <cstdlib>
+#include <cerrno>
 
 #include "TObjectTable.h"
 #include "TError.h"
diff --git a/core/rint/src/TRint.cxx b/core/rint/src/TRint.cxx
index 12b33fac26384..7a29449a94e72 100644
--- a/core/rint/src/TRint.cxx
+++ b/core/rint/src/TRint.cxx
@@ -47,7 +47,7 @@
 #include "snprintf.h"
 
 #ifdef R__UNIX
-#include <signal.h>
+#include <csignal>
 #include <unistd.h>
 #endif
 
diff --git a/core/textinput/src/textinput/History.cpp b/core/textinput/src/textinput/History.cpp
index e186842970908..10aebc97af4a9 100644
--- a/core/textinput/src/textinput/History.cpp
+++ b/core/textinput/src/textinput/History.cpp
@@ -19,7 +19,7 @@
 #include <sstream>
 
 #ifdef WIN32
-# include <stdio.h>
+# include <cstdio>
 extern "C" unsigned long __stdcall GetCurrentProcessId(void);
 #else
 # include <unistd.h>
diff --git a/core/textinput/src/textinput/KeyBinding.cpp b/core/textinput/src/textinput/KeyBinding.cpp
index 2477669d3c20a..4871bd3a845b1 100644
--- a/core/textinput/src/textinput/KeyBinding.cpp
+++ b/core/textinput/src/textinput/KeyBinding.cpp
@@ -14,7 +14,7 @@
 
 #include "textinput/KeyBinding.h"
 
-#include <ctype.h>
+#include <cctype>
 
 namespace textinput {
   KeyBinding::KeyBinding(): fEscPending(false), fEscCmdEnabled(false) {}
diff --git a/core/textinput/src/textinput/StreamReaderUnix.cpp b/core/textinput/src/textinput/StreamReaderUnix.cpp
index 14d08ff55602e..7b900f87fec44 100644
--- a/core/textinput/src/textinput/StreamReaderUnix.cpp
+++ b/core/textinput/src/textinput/StreamReaderUnix.cpp
@@ -21,9 +21,9 @@
 #include <sys/time.h>
 #include <unistd.h>
 #include <termios.h>
-#include <stdio.h>
+#include <cstdio>
 #ifdef __APPLE__
-#include <errno.h> // For EINTR
+#include <cerrno> // For EINTR
 #endif
 
 #include <cctype>
diff --git a/core/textinput/src/textinput/StreamReaderWin.cpp b/core/textinput/src/textinput/StreamReaderWin.cpp
index 538ca111c8817..fd6d6d5a7477d 100644
--- a/core/textinput/src/textinput/StreamReaderWin.cpp
+++ b/core/textinput/src/textinput/StreamReaderWin.cpp
@@ -17,7 +17,7 @@
 #include "textinput/StreamReaderWin.h"
 
 #include <io.h>
-#include <stdio.h>
+#include <cstdio>
 #include <Windows.h>
 
 // MSVC 7.1 is missing these definitions:
diff --git a/core/textinput/src/textinput/TerminalConfigUnix.cpp b/core/textinput/src/textinput/TerminalConfigUnix.cpp
index e23106139d7e7..8d9a36ce2ec37 100644
--- a/core/textinput/src/textinput/TerminalConfigUnix.cpp
+++ b/core/textinput/src/textinput/TerminalConfigUnix.cpp
@@ -21,7 +21,7 @@
 
 #include <termios.h>
 #include <unistd.h>
-#include <stdio.h>
+#include <cstdio>
 #include <cstring>
 
 using namespace textinput;
diff --git a/core/textinput/src/textinput/TerminalDisplayWin.cpp b/core/textinput/src/textinput/TerminalDisplayWin.cpp
index 5d3e1939f34b6..a3fc5cc811b89 100644
--- a/core/textinput/src/textinput/TerminalDisplayWin.cpp
+++ b/core/textinput/src/textinput/TerminalDisplayWin.cpp
@@ -17,7 +17,7 @@
 #include "textinput/TerminalDisplayWin.h"
 #include "textinput/Color.h"
 
-#include <assert.h>
+#include <cassert>
 
 #ifdef UNICODE
 #define filename L"CONOUT$"
diff --git a/core/thread/inc/PosixThreadInc.h b/core/thread/inc/PosixThreadInc.h
index 24003f8fdcfc9..1f3c8b2c42ca9 100644
--- a/core/thread/inc/PosixThreadInc.h
+++ b/core/thread/inc/PosixThreadInc.h
@@ -20,7 +20,7 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include <stdlib.h>
-#include <time.h>
+#include <cstdlib>
+#include <ctime>
 
 #endif
diff --git a/core/thread/inc/TThread.h b/core/thread/inc/TThread.h
index 65e082e141f88..da08e533fc52d 100644
--- a/core/thread/inc/TThread.h
+++ b/core/thread/inc/TThread.h
@@ -26,7 +26,7 @@
 
 #include "TNamed.h"
 #include "TTimer.h"
-#include <stdarg.h>
+#include <cstdarg>
 
 #ifdef R__LESS_INCLUDES
 class TCondition;
diff --git a/core/thread/src/TMutex.cxx b/core/thread/src/TMutex.cxx
index 5662435f07e8c..ac62295888ad2 100644
--- a/core/thread/src/TMutex.cxx
+++ b/core/thread/src/TMutex.cxx
@@ -22,7 +22,7 @@
 #include "TInterpreter.h"
 #include "TMutex.h"
 #include "TThreadFactory.h"
-#include <errno.h>
+#include <cerrno>
 #include "TError.h"
 
 ClassImp(TMutex);
diff --git a/core/thread/src/TPosixCondition.cxx b/core/thread/src/TPosixCondition.cxx
index 5aaed1488f667..ae536b372da1f 100644
--- a/core/thread/src/TPosixCondition.cxx
+++ b/core/thread/src/TPosixCondition.cxx
@@ -22,7 +22,7 @@
 #include "TPosixMutex.h"
 #include "PosixThreadInc.h"
 
-#include <errno.h>
+#include <cerrno>
 
 
 ClassImp(TPosixCondition);
diff --git a/core/thread/src/TReentrantRWLock.cxx b/core/thread/src/TReentrantRWLock.cxx
index e18ec0e466c07..1e19c3dd70e2c 100644
--- a/core/thread/src/TReentrantRWLock.cxx
+++ b/core/thread/src/TReentrantRWLock.cxx
@@ -35,7 +35,7 @@ thus preventing starvation.
 #include "ROOT/TSpinMutex.hxx"
 #include "TMutex.h"
 #include "TError.h"
-#include <assert.h>
+#include <cassert>
 
 using namespace ROOT;
 
diff --git a/core/thread/src/TWin32Condition.cxx b/core/thread/src/TWin32Condition.cxx
index f2f1a1e3216d7..cfeb74e5f980c 100644
--- a/core/thread/src/TWin32Condition.cxx
+++ b/core/thread/src/TWin32Condition.cxx
@@ -23,7 +23,7 @@
 #include "TTimeStamp.h"
 #include "Windows4Root.h"
 
-#include <errno.h>
+#include <cerrno>
 
 ClassImp(TWin32Condition);
 
diff --git a/core/thread/src/TWin32Thread.cxx b/core/thread/src/TWin32Thread.cxx
index 694e3488db507..5de916fe4d820 100644
--- a/core/thread/src/TWin32Thread.cxx
+++ b/core/thread/src/TWin32Thread.cxx
@@ -22,7 +22,7 @@
 #include "TThread.h"
 
 #include <process.h>
-#include <errno.h>
+#include <cerrno>
 
 ClassImp(TWin32Thread);
 
diff --git a/core/unix/CMakeLists.txt b/core/unix/CMakeLists.txt
index 9e432095f3c8f..9f76985a8c54a 100644
--- a/core/unix/CMakeLists.txt
+++ b/core/unix/CMakeLists.txt
@@ -20,7 +20,7 @@ if (CMAKE_SYSTEM_NAME MATCHES FreeBSD)
   target_link_libraries(Core PRIVATE execinfo util)
 endif()
 
-CHECK_CXX_SOURCE_COMPILES("#include <stdlib.h>
+CHECK_CXX_SOURCE_COMPILES("#include <cstdlib>
 int main() { char buf[32]; arc4random_buf(buf, 32); return 0;}" found_arc4)
 
 if(found_arc4)
diff --git a/core/unix/src/TUnixSystem.cxx b/core/unix/src/TUnixSystem.cxx
index 96be304d40302..fa2dd22e960cb 100644
--- a/core/unix/src/TUnixSystem.cxx
+++ b/core/unix/src/TUnixSystem.cxx
@@ -94,15 +94,15 @@
 #include <utime.h>
 #include <syslog.h>
 #include <sys/stat.h>
-#include <setjmp.h>
-#include <signal.h>
+#include <csetjmp>
+#include <csignal>
 #include <sys/param.h>
 #include <pwd.h>
 #include <grp.h>
-#include <errno.h>
+#include <cerrno>
 #include <sys/resource.h>
 #include <sys/wait.h>
-#include <time.h>
+#include <ctime>
 #include <sys/time.h>
 #include <sys/file.h>
 #include <sys/socket.h>
@@ -218,7 +218,7 @@ extern "C" {
 
 // FPE handling includes
 #if (defined(R__LINUX) && !defined(R__WINGCC))
-#include <fenv.h>
+#include <cfenv>
 #include <sys/prctl.h>    // for prctl() function used in StackTrace()
 #endif
 
@@ -229,11 +229,11 @@ extern "C" {
 #if defined(R__MACOSX) && !defined(__SSE2__) && !defined(__xlC__) && \
    !defined(__i386__) && !defined(__x86_64__) && !defined(__arm__) && \
    !defined(__arm64__)
-#include <fenv.h>
-#include <signal.h>
+#include <cfenv>
+#include <csignal>
 #include <ucontext.h>
-#include <stdlib.h>
-#include <stdio.h>
+#include <cstdlib>
+#include <cstdio>
 #include <mach/thread_status.h>
 
 #define fegetenvd(x) asm volatile("mffs %0" : "=f" (x));
@@ -251,7 +251,7 @@ enum {
 
 #if defined(R__MACOSX) && !defined(__SSE2__) && \
     (defined(__i386__) || defined(__x86_64__) || defined(__arm__) || defined(__arm64__))
-#include <fenv.h>
+#include <cfenv>
 #endif
 // End FPE handling includes
 
diff --git a/core/winnt/src/TWinNTSystem.cxx b/core/winnt/src/TWinNTSystem.cxx
index 820d8c5367ce6..0a618b2906061 100644
--- a/core/winnt/src/TWinNTSystem.cxx
+++ b/core/winnt/src/TWinNTSystem.cxx
@@ -47,8 +47,8 @@
 #include <process.h>
 #include <io.h>
 #include <direct.h>
-#include <ctype.h>
-#include <float.h>
+#include <cctype>
+#include <cfloat>
 #include <sys/stat.h>
 #include <csignal>
 #include <cstdio>
diff --git a/documentation/doxygen/filter.cxx b/documentation/doxygen/filter.cxx
index bcf606ef52373..a70674739b7ee 100644
--- a/documentation/doxygen/filter.cxx
+++ b/documentation/doxygen/filter.cxx
@@ -80,7 +80,7 @@
 /// python documentation.
 
 #include <unistd.h>
-#include <stdio.h>
+#include <cstdio>
 #include <string>
 #include <cstring>
 #include <iostream>
diff --git a/documentation/doxygen/makeimage.C b/documentation/doxygen/makeimage.C
index 9574dc2ce0225..a39cf39de44c1 100644
--- a/documentation/doxygen/makeimage.C
+++ b/documentation/doxygen/makeimage.C
@@ -9,7 +9,7 @@
 #include <TString.h>
 #include <TSystem.h>
 
-#include <stdio.h>
+#include <cstdio>
 
 void FindImageInPad(TPad *P)
 {
diff --git a/documentation/primer/macros/ExampleMacro.C b/documentation/primer/macros/ExampleMacro.C
index 8c299abbf95cd..f7fb730a8c7d2 100644
--- a/documentation/primer/macros/ExampleMacro.C
+++ b/documentation/primer/macros/ExampleMacro.C
@@ -22,7 +22,7 @@
 #include "TCanvas.h"
 #include "TMath.h"
 // eventually, load some C libraries
-#include <math.h>
+#include <cmath>
 
 void ExampleMacro();
 
diff --git a/documentation/primer/macros/ExampleMacro_GUI.C b/documentation/primer/macros/ExampleMacro_GUI.C
index 9062fef046f17..13f6550cfb302 100644
--- a/documentation/primer/macros/ExampleMacro_GUI.C
+++ b/documentation/primer/macros/ExampleMacro_GUI.C
@@ -12,7 +12,7 @@
 #include "TMath.h"
 
 // eventually, include some additoinal C or C++ libraries
-#include <math.h>
+#include <cmath>
 
 //     ==>>  put the code of your macro here
 void ExampleMacro_GUI() {
diff --git a/documentation/users-guide/ALittleC++.md b/documentation/users-guide/ALittleC++.md
index bd09d528d6dc6..2308f565121ec 100644
--- a/documentation/users-guide/ALittleC++.md
+++ b/documentation/users-guide/ALittleC++.md
@@ -235,7 +235,7 @@ equation `ax**2 + bx +c = 0`.
 
 ``` {.cpp}
    #include <iostream.h>
-   #include <math.h>
+   #include <cmath>
    #include "Quad.h"
 
    Quad::Quad(Float_t a, Float_t b, Float_t c) {
diff --git a/graf3d/eve7/src/REveGluTess.cxx b/graf3d/eve7/src/REveGluTess.cxx
index caa8154079720..a9e24603f1dd4 100644
--- a/graf3d/eve7/src/REveGluTess.cxx
+++ b/graf3d/eve7/src/REveGluTess.cxx
@@ -25,8 +25,8 @@
 
 #include <ROOT/REveGluTess.hxx>
 
-#include <math.h>
-#include <stdlib.h>
+#include <cmath>
+#include <cstdlib>
 #include <stdexcept>
 
 namespace ROOT {
diff --git a/graf3d/ftgl/src/FTExtrdGlyph.cxx b/graf3d/ftgl/src/FTExtrdGlyph.cxx
index 35da4e150d1f6..82fefb4b885b0 100644
--- a/graf3d/ftgl/src/FTExtrdGlyph.cxx
+++ b/graf3d/ftgl/src/FTExtrdGlyph.cxx
@@ -1,6 +1,6 @@
 #include <iostream>
 
-#include    <math.h>
+#include    <cmath>
 
 #include    "FTExtrdGlyph.h"
 #include    "FTVectoriser.h"
diff --git a/graf3d/gl/src/gl2ps.cxx b/graf3d/gl/src/gl2ps.cxx
index 126fd69885675..de21e664871c7 100644
--- a/graf3d/gl/src/gl2ps.cxx
+++ b/graf3d/gl/src/gl2ps.cxx
@@ -58,12 +58,12 @@
 
 #include "gl2ps.h"
 
-#include <math.h>
-#include <string.h>
+#include <cmath>
+#include <cstring>
 #include <sys/types.h>
-#include <stdarg.h>
-#include <time.h>
-#include <float.h>
+#include <cstdarg>
+#include <ctime>
+#include <cfloat>
 #include <string>
 
 #if defined(GL2PS_HAVE_ZLIB)
diff --git a/gui/browserv7/inc/ROOT/RFileDialog.hxx b/gui/browserv7/inc/ROOT/RFileDialog.hxx
index 0a46d866589c5..8b42beb587a82 100644
--- a/gui/browserv7/inc/ROOT/RFileDialog.hxx
+++ b/gui/browserv7/inc/ROOT/RFileDialog.hxx
@@ -17,7 +17,7 @@
 
 #include <vector>
 #include <memory>
-#include <stdint.h>
+#include <cstdint>
 
 namespace ROOT {
 
diff --git a/gui/gui/src/TGRedirectOutputGuard.cxx b/gui/gui/src/TGRedirectOutputGuard.cxx
index 4847f4108bd57..5ddd407e192a7 100644
--- a/gui/gui/src/TGRedirectOutputGuard.cxx
+++ b/gui/gui/src/TGRedirectOutputGuard.cxx
@@ -42,7 +42,7 @@ Optionally the output can also be saved into a file:
 */
 
 
-#include <errno.h>
+#include <cerrno>
 #include <sys/types.h>
 #ifdef WIN32
 #   include <io.h>
diff --git a/gui/guihtml/src/TGHtmlElement.cxx b/gui/guihtml/src/TGHtmlElement.cxx
index afc16fd082694..8904a62bb3631 100644
--- a/gui/guihtml/src/TGHtmlElement.cxx
+++ b/gui/guihtml/src/TGHtmlElement.cxx
@@ -31,7 +31,7 @@
 
 **************************************************************************/
 
-#include <string.h>
+#include <cstring>
 
 #include "TGHtml.h"
 #include "TImage.h"
diff --git a/gui/guihtml/src/TGHtmlLayout.cxx b/gui/guihtml/src/TGHtmlLayout.cxx
index 37d6de602ca80..c39155dd7db94 100644
--- a/gui/guihtml/src/TGHtmlLayout.cxx
+++ b/gui/guihtml/src/TGHtmlLayout.cxx
@@ -26,8 +26,8 @@
 // This file contains the code used to position elements of the
 // HTML file on the screen.
 
-#include <stdlib.h>
-#include <string.h>
+#include <cstdlib>
+#include <cstring>
 
 #include "TGHtml.h"
 
diff --git a/gui/guihtml/src/TGHtmlUri.cxx b/gui/guihtml/src/TGHtmlUri.cxx
index 80082c622b438..2dd147aca9ffa 100644
--- a/gui/guihtml/src/TGHtmlUri.cxx
+++ b/gui/guihtml/src/TGHtmlUri.cxx
@@ -33,7 +33,7 @@
 
 // Routines for processing URLs.
 
-#include <ctype.h>
+#include <cctype>
 #include <cstring>
 #include <cstdlib>
 
diff --git a/gui/webdisplay/src/RWebDisplayHandle.cxx b/gui/webdisplay/src/RWebDisplayHandle.cxx
index f0266c34a50b7..dfcd2632946c7 100644
--- a/gui/webdisplay/src/RWebDisplayHandle.cxx
+++ b/gui/webdisplay/src/RWebDisplayHandle.cxx
@@ -37,8 +37,8 @@
 #include <process.h>
 #else
 #include <unistd.h>
-#include <stdlib.h>
-#include <signal.h>
+#include <cstdlib>
+#include <csignal>
 #include <spawn.h>
 #ifdef R__MACOSX
 #include <sys/wait.h>
diff --git a/gui/webdisplay/src/RWebWindow.cxx b/gui/webdisplay/src/RWebWindow.cxx
index ca44d36ed8aed..d97db4d368518 100644
--- a/gui/webdisplay/src/RWebWindow.cxx
+++ b/gui/webdisplay/src/RWebWindow.cxx
@@ -25,7 +25,7 @@
 #include <cstring>
 #include <cstdlib>
 #include <utility>
-#include <assert.h>
+#include <cassert>
 #include <algorithm>
 #include <fstream>
 
diff --git a/io/dcache/src/TDCacheFile.cxx b/io/dcache/src/TDCacheFile.cxx
index 0a10c5dbaac60..7b3819e2d1b18 100644
--- a/io/dcache/src/TDCacheFile.cxx
+++ b/io/dcache/src/TDCacheFile.cxx
@@ -28,7 +28,7 @@ TFile behaviour.
 #include "TROOT.h"
 
 #include <cstdlib>
-#include <errno.h>
+#include <cerrno>
 #include <sys/stat.h>
 #include <sys/types.h>
 
diff --git a/io/io/inc/TMakeProject.h b/io/io/inc/TMakeProject.h
index ae56c2663171b..32577896dfefd 100644
--- a/io/io/inc/TMakeProject.h
+++ b/io/io/inc/TMakeProject.h
@@ -12,7 +12,7 @@
 #ifndef ROOT_TMakeProject
 #define ROOT_TMakeProject
 
-#include <stdio.h>
+#include <cstdio>
 #include "TString.h"
 
 class TList;
diff --git a/io/io/src/TArchiveFile.cxx b/io/io/src/TArchiveFile.cxx
index ece2b54b9e6df..259a522f84534 100644
--- a/io/io/src/TArchiveFile.cxx
+++ b/io/io/src/TArchiveFile.cxx
@@ -25,7 +25,7 @@ or TAR archive.
 #include "TObjString.h"
 #include "TError.h"
 #include "TUrl.h"
-#include <stdlib.h>
+#include <cstdlib>
 
 
 ClassImp(TArchiveFile);
diff --git a/io/io/src/TBufferFile.cxx b/io/io/src/TBufferFile.cxx
index a6248a808f9a8..56c48fc216ec5 100644
--- a/io/io/src/TBufferFile.cxx
+++ b/io/io/src/TBufferFile.cxx
@@ -17,7 +17,7 @@
 The concrete implementation of TBuffer for writing/reading to/from a ROOT file or socket.
 */
 
-#include <string.h>
+#include <cstring>
 #include <typeinfo>
 #include <string>
 #include <limits>
diff --git a/io/io/src/TBufferJSON.cxx b/io/io/src/TBufferJSON.cxx
index 8f5c8989cf6e7..e4e1add1cb330 100644
--- a/io/io/src/TBufferJSON.cxx
+++ b/io/io/src/TBufferJSON.cxx
@@ -102,7 +102,7 @@ class Container {
 #include <typeinfo>
 #include <string>
 #include <cstring>
-#include <locale.h>
+#include <clocale>
 #include <cmath>
 #include <memory>
 #include <cstdlib>
diff --git a/io/io/src/TContainerConverters.cxx b/io/io/src/TContainerConverters.cxx
index 4e89661dfd484..a6beb49f53433 100644
--- a/io/io/src/TContainerConverters.cxx
+++ b/io/io/src/TContainerConverters.cxx
@@ -31,7 +31,7 @@
 #include "TError.h"
 #include "TGenCollectionStreamer.h"
 #include "TClassStreamer.h"
-#include <stdlib.h>
+#include <cstdlib>
 
 namespace {
    const Int_t  kMapOffset = 2;
diff --git a/io/io/src/TFile.cxx b/io/io/src/TFile.cxx
index 43e3818f4e311..677035e2e302c 100644
--- a/io/io/src/TFile.cxx
+++ b/io/io/src/TFile.cxx
@@ -90,7 +90,7 @@ The structure of a directory is shown in TDirectoryFile::TDirectoryFile
 #endif
 #endif
 #include <fcntl.h>
-#include <errno.h>
+#include <cerrno>
 #include <sys/stat.h>
 #ifndef WIN32
 #include <unistd.h>
@@ -151,7 +151,7 @@ The structure of a directory is shown in TDirectoryFile::TDirectoryFile
 #include "TGlobal.h"
 #include "ROOT/RConcurrentHashColl.hxx"
 #include <memory>
-#include <inttypes.h>
+#include <cinttypes>
 
 #ifdef R__FBSD
 #include <sys/extattr.h>
diff --git a/io/io/src/TLockFile.cxx b/io/io/src/TLockFile.cxx
index 064a9b5c9ba59..2f5ecb3b38ec4 100644
--- a/io/io/src/TLockFile.cxx
+++ b/io/io/src/TLockFile.cxx
@@ -29,7 +29,7 @@ Use it in scope-blocks like:
 #include "TLockFile.h"
 #include "TSystem.h"
 #include "TFile.h"
-#include <time.h>
+#include <ctime>
 
 ClassImp(TLockFile);
 
diff --git a/io/io/src/TMakeProject.cxx b/io/io/src/TMakeProject.cxx
index 62b7baae23b26..dcec5cdff56e0 100644
--- a/io/io/src/TMakeProject.cxx
+++ b/io/io/src/TMakeProject.cxx
@@ -16,7 +16,7 @@
 Helper class implementing the TFile::MakeProject.
 **/
 
-#include <ctype.h>
+#include <cctype>
 #include "TMakeProject.h"
 #include "TClass.h"
 #include "TClassEdit.h"
diff --git a/io/io/src/TMapFile.cxx b/io/io/src/TMapFile.cxx
index 1bba942f7e240..c3eb70f3cb1ad 100644
--- a/io/io/src/TMapFile.cxx
+++ b/io/io/src/TMapFile.cxx
@@ -85,7 +85,7 @@ robust Streamer mechanism I opted for 3).
 #endif
 
 #include <fcntl.h>
-#include <errno.h>
+#include <cerrno>
 
 #include "TMapFile.h"
 #include "TKeyMapFile.h"
diff --git a/io/io/src/TMemFile.cxx b/io/io/src/TMemFile.cxx
index 728981a182ac4..1025da9253324 100644
--- a/io/io/src/TMemFile.cxx
+++ b/io/io/src/TMemFile.cxx
@@ -27,8 +27,8 @@ only from memory.
 #include "TKey.h"
 #include "TClass.h"
 #include "TVirtualMutex.h"
-#include <errno.h>
-#include <stdio.h>
+#include <cerrno>
+#include <cstdio>
 #include <sys/stat.h>
 
 // The following snippet is used for developer-level debugging
diff --git a/io/io/test/TMapFileTest.cxx b/io/io/test/TMapFileTest.cxx
index 23f5fa760d3db..fc736e72f4a2d 100644
--- a/io/io/test/TMapFileTest.cxx
+++ b/io/io/test/TMapFileTest.cxx
@@ -1,5 +1,5 @@
 #include <atomic>
-#include <stdio.h>
+#include <cstdio>
 #include <future>
 #include <thread>
 
diff --git a/io/sql/inc/TSQLFile.h b/io/sql/inc/TSQLFile.h
index 7c26c41bb9c3f..6212462db8621 100644
--- a/io/sql/inc/TSQLFile.h
+++ b/io/sql/inc/TSQLFile.h
@@ -13,7 +13,7 @@
 #define ROOT_TSQLFile
 
 #include "TFile.h"
-#include <stdlib.h>
+#include <cstdlib>
 
 class TList;
 class TStreamerElement;
diff --git a/main/src/cppmain.cxx b/main/src/cppmain.cxx
index c7a2554b57bd2..6ccc431a2cbac 100644
--- a/main/src/cppmain.cxx
+++ b/main/src/cppmain.cxx
@@ -19,7 +19,7 @@
  * representations about the suitability of this software for any
  * purpose.  It is provided "as is" without express or implied warranty.
  ************************************************************************/
-#include <stdio.h>
+#include <cstdio>
 
 extern "C" {
 extern void G__setothermain(int othermain);
diff --git a/main/src/roots.cxx b/main/src/roots.cxx
index a90d0ec994fc5..b8470293678ae 100644
--- a/main/src/roots.cxx
+++ b/main/src/roots.cxx
@@ -15,11 +15,11 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include <stdio.h>
+#include <cstdio>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
-#include <errno.h>
+#include <cerrno>
 
 #include "TInterpreter.h"
 #include "TROOT.h"
diff --git a/math/mathcore/inc/Math/Math.h b/math/mathcore/inc/Math/Math.h
index 2db820667693f..86ecb85bfe650 100644
--- a/math/mathcore/inc/Math/Math.h
+++ b/math/mathcore/inc/Math/Math.h
@@ -21,7 +21,8 @@
 
 #if defined(__sun) || defined(_MSC_VER)
 //Microsoft and solaris definition of cmath does not include math.h which has the definitions of numerical constants
-#include <math.h>
+#include <math.h> // for M_PI
+// TODO replace with std::numbers::pi once minimum version is C++20, and remove this code block
 #endif
 
 
diff --git a/math/mathcore/inc/Math/TDataPoint.h b/math/mathcore/inc/Math/TDataPoint.h
index c0821508bf57a..9a5ad69c4985a 100644
--- a/math/mathcore/inc/Math/TDataPoint.h
+++ b/math/mathcore/inc/Math/TDataPoint.h
@@ -17,7 +17,7 @@
 #include "RtypesCore.h"
 
 #include <cassert>
-#include <math.h>
+#include <cmath>
 
 namespace ROOT {
 namespace Math {
diff --git a/math/minuit2/doc/Minuit2.md b/math/minuit2/doc/Minuit2.md
index 7c654fa41a51b..0428c2390e3b5 100644
--- a/math/minuit2/doc/Minuit2.md
+++ b/math/minuit2/doc/Minuit2.md
@@ -1867,7 +1867,7 @@ The user's model function is a Gaussian.
     #ifndef MN_GaussFunction_H_
     #define MN_GaussFunction_H_
 
-    #include <math.h>
+    #include <cmath>
 
     class GaussFunction {
 
diff --git a/math/smatrix/inc/Math/MConfig.h b/math/smatrix/inc/Math/MConfig.h
index f74e429da92f8..f10d87f5911a7 100644
--- a/math/smatrix/inc/Math/MConfig.h
+++ b/math/smatrix/inc/Math/MConfig.h
@@ -5,7 +5,7 @@
 #define ROOT_Math_MConfig
 
 #if defined(__sun) && !defined(linux)
-#include <stdlib.h>
+#include <cstdlib>
 // Solaris does not support expression like D1*(D1+1)/2 as template parameters
 #define UNSUPPORTED_TEMPLATE_EXPRESSION
 #endif
diff --git a/math/smatrix/inc/Math/SMatrix.icc b/math/smatrix/inc/Math/SMatrix.icc
index 75759e921aa01..6d01126158186 100644
--- a/math/smatrix/inc/Math/SMatrix.icc
+++ b/math/smatrix/inc/Math/SMatrix.icc
@@ -40,7 +40,7 @@
 
 #include <iostream>
 #include <iomanip>
-#include <assert.h>
+#include <cassert>
 //#ifndef ROOT_Math_Dsinv
 //#include "Math/Dsinv.h"
 //#endif
diff --git a/math/smatrix/inc/Math/SVector.icc b/math/smatrix/inc/Math/SVector.icc
index 7ae737e753010..2de27e35fcd6a 100644
--- a/math/smatrix/inc/Math/SVector.icc
+++ b/math/smatrix/inc/Math/SVector.icc
@@ -36,7 +36,7 @@
 #endif // ROOT_Math_SVector
 
 #include <iostream>
-#include <assert.h>
+#include <cassert>
 #include <algorithm>
 
 #include "Math/StaticCheck.h"
diff --git a/math/unuran/config.h.win.in b/math/unuran/config.h.win.in
index 0ce9dfc6aa5d9..6db927ee07db4 100644
--- a/math/unuran/config.h.win.in
+++ b/math/unuran/config.h.win.in
@@ -52,7 +52,7 @@
 /* Define to 1 if you have the <dlfcn.h> header file. */
 /* #undef HAVE_DLFCN_H */
 
-/* Define to 1 if you have the <float.h> header file. */
+/* Define to 1 if you have the <cfloat> header file. */
 #define HAVE_FLOAT_H 1
 
 /* Define to 1 if you have the `floor' function. */
@@ -67,7 +67,7 @@
 /* Define to 1 if "x != x" is true for NaNs */
 #define HAVE_IEEE_COMPARISONS 1
 
-/* Define to 1 if you have the <inttypes.h> header file. */
+/* Define to 1 if you have the <cinttypes> header file. */
 /* #undef HAVE_INTTYPES_H */
 
 /* Define to 1 if you have the `gsl' library (-lgsl). */
@@ -85,7 +85,7 @@
 /* Define to 1 if you have the `rngstreams' library (-lrngstreams). */
 /* #undef HAVE_LIBRNGSTREAMS */
 
-/* Define to 1 if you have the <limits.h> header file. */
+/* Define to 1 if you have the <climits> header file. */
 #define HAVE_LIMITS_H 1
 
 /* Define to 1 if you have the <memory.h> header file. */
@@ -106,10 +106,10 @@
 /* Define to 1 if you have the `sqrt' function. */
 #define HAVE_SQRT 1
 
-/* Define to 1 if you have the <stdint.h> header file. */
+/* Define to 1 if you have the <cstdint> header file. */
 /* #undef HAVE_STDINT_H */
 
-/* Define to 1 if you have the <stdlib.h> header file. */
+/* Define to 1 if you have the <cstdlib> header file. */
 #define HAVE_STDLIB_H 1
 
 /* Define to 1 if you have the `strcasecmp' function. */
@@ -121,7 +121,7 @@
 /* Define to 1 if you have the <strings.h> header file. */
 /* #undef HAVE_STRINGS_H */
 
-/* Define to 1 if you have the <string.h> header file. */
+/* Define to 1 if you have the <cstring> header file. */
 #define HAVE_STRING_H 1
 
 /* Define to 1 if you have the `strtol' function. */
@@ -170,7 +170,7 @@
 /* Define to 1 if you have the ANSI C header files. */
 #define STDC_HEADERS 1
 
-/* Define to 1 if you can safely include both <sys/time.h> and <time.h>. */
+/* Define to 1 if you can safely include both <sys/time.h> and <ctime>. */
 /* #undef TIME_WITH_SYS_TIME */
 
 /* Define to 1 if you use random number generators from GNU Scientific
diff --git a/math/vecops/inc/ROOT/RVec.hxx b/math/vecops/inc/ROOT/RVec.hxx
index b33235286090a..1767add52a2b6 100644
--- a/math/vecops/inc/ROOT/RVec.hxx
+++ b/math/vecops/inc/ROOT/RVec.hxx
@@ -24,7 +24,8 @@
       #ifndef _USE_MATH_DEFINES
          #define _USE_MATH_DEFINES
       #endif
-      #include <math.h>
+      #include <math.h> // for M_PI
+      // TODO once minimum standard is C++20: replace with std::numbers::pi and remove this codeblock
       #undef _USE_MATH_DEFINES
    #endif
    #define _VECOPS_USE_EXTERN_TEMPLATES false
diff --git a/misc/win/bindexplib/bindexplib.cxx b/misc/win/bindexplib/bindexplib.cxx
index 2819d339e4c5b..3c67b94c26e60 100644
--- a/misc/win/bindexplib/bindexplib.cxx
+++ b/misc/win/bindexplib/bindexplib.cxx
@@ -66,7 +66,7 @@
 #include <windows.h>
 
 #include <set>
-#include <stdio.h>
+#include <cstdio>
 #include <string>
 #include <fstream>
 
diff --git a/montecarlo/eg/inc/cfortran.h b/montecarlo/eg/inc/cfortran.h
index d44e1cef15f56..1416f39a5fabc 100644
--- a/montecarlo/eg/inc/cfortran.h
+++ b/montecarlo/eg/inc/cfortran.h
@@ -114,10 +114,10 @@
 #define VAXUltrix
 #endif
 
-#include <stdio.h>     /* NULL [in all machines stdio.h]                      */
-#include <string.h>    /* strlen, memset, memcpy, memchr.                     */
+#include <cstdio>     /* NULL [in all machines stdio.h]                      */
+#include <cstring>    /* strlen, memset, memcpy, memchr.                     */
 #if !( defined(VAXUltrix) || defined(sun) || (defined(apollo)&&!defined(__STDCPP__)) )
-#include <stdlib.h>    /* malloc,free                                         */
+#include <cstdlib>    /* malloc,free                                         */
 #else
 #include <malloc.h>    /* Had to be removed for DomainOS h105 10.4 sys5.3 425t*/
 #ifdef apollo
@@ -348,13 +348,13 @@ only C calling FORTRAN subroutines will work using K&R style.*/
 
 #ifdef sunFortran
 #if defined(sun) || defined(__sun)
-#include <math.h>     /* Sun's FLOATFUNCTIONTYPE, ASSIGNFLOAT, RETURNFLOAT.  */
+#include <cmath>     /* Sun's FLOATFUNCTIONTYPE, ASSIGNFLOAT, RETURNFLOAT.  */
 #else
 #include "math.h"     /* i.e. if crosscompiling assume user has file. */
 #endif
 /* At least starting with the default C compiler SC3.0.1 of SunOS 5.3,
  * FLOATFUNCTIONTYPE, ASSIGNFLOAT, RETURNFLOAT are not required and not in
- * <math.h>, since sun C no longer promotes C float return values to doubles.
+ * <cmath>, since sun C no longer promotes C float return values to doubles.
  * Therefore, only use them if defined.
  * Even if gcc is being used, assume that it exhibits the Sun C compiler
  * behavior in order to be able to use *.o from the Sun C compiler.
diff --git a/montecarlo/eg/src/TDatabasePDG.cxx b/montecarlo/eg/src/TDatabasePDG.cxx
index 3c0b0ca2c9f2a..0aa1a2e63f86b 100644
--- a/montecarlo/eg/src/TDatabasePDG.cxx
+++ b/montecarlo/eg/src/TDatabasePDG.cxx
@@ -18,7 +18,7 @@
 #include "TDatabasePDG.h"
 #include "TDecayChannel.h"
 #include "TParticlePDG.h"
-#include <stdlib.h>
+#include <cstdlib>
 
 
 /** \class TDatabasePDG
diff --git a/net/auth/res/rsafun.h b/net/auth/res/rsafun.h
index ddd2d7685b62c..4bf99869b2965 100644
--- a/net/auth/res/rsafun.h
+++ b/net/auth/res/rsafun.h
@@ -31,7 +31,7 @@ MA  02110-1301  USA
 *                                                                              *
 *******************************************************************************/
 
-#include <stdio.h>
+#include <cstdio>
 
 #ifndef ROOT_rsafun
 #define ROOT_rsafun
diff --git a/net/auth/res/rsalib.h b/net/auth/res/rsalib.h
index 8086c50af62f8..b1a463e7804e5 100644
--- a/net/auth/res/rsalib.h
+++ b/net/auth/res/rsalib.h
@@ -36,7 +36,7 @@ MA  02110-1301  USA
 
 #include "rsadef.h"
 
-#include <stdio.h>
+#include <cstdio>
 
 rsa_NUMBER rsa_genprim(int, int);
 int    rsa_genrsa(rsa_NUMBER, rsa_NUMBER, rsa_NUMBER *, rsa_NUMBER *, rsa_NUMBER *);
diff --git a/net/auth/src/TAuthenticate.cxx b/net/auth/src/TAuthenticate.cxx
index 39ecad52c84f7..c28fea0cd6711 100644
--- a/net/auth/src/TAuthenticate.cxx
+++ b/net/auth/src/TAuthenticate.cxx
@@ -46,9 +46,9 @@
 #ifndef R__LYNXOS
 #include <sys/stat.h>
 #endif
-#include <errno.h>
+#include <cerrno>
 #include <sys/types.h>
-#include <time.h>
+#include <ctime>
 #if !defined(R__WIN32) && !defined(R__MACOSX) && !defined(R__FBSD) && \
     !defined(R__OBSD)
 #include <crypt.h>
@@ -59,7 +59,7 @@
 #if defined(R__LINUX) || defined(R__FBSD) || defined(R__OBSD)
 #  include <unistd.h>
 #endif
-#include <stdlib.h>
+#include <cstdlib>
 #ifndef WIN32
 #  include <sys/time.h>
 #endif /* WIN32 */
diff --git a/net/auth/src/THostAuth.cxx b/net/auth/src/THostAuth.cxx
index d7491b84dc2e7..689926d7a9bb5 100644
--- a/net/auth/src/THostAuth.cxx
+++ b/net/auth/src/THostAuth.cxx
@@ -26,7 +26,7 @@
 #include "TAuthenticate.h"
 #include "TSocket.h"
 #include "TUrl.h"
-#include <stdlib.h>
+#include <cstdlib>
 
 
 ClassImp(THostAuth);
diff --git a/net/auth/src/TRootSecContext.cxx b/net/auth/src/TRootSecContext.cxx
index c3ac5b9cd7130..aed99db68935d 100644
--- a/net/auth/src/TRootSecContext.cxx
+++ b/net/auth/src/TRootSecContext.cxx
@@ -19,7 +19,7 @@
 
 #include "RConfigure.h"
 
-#include <stdlib.h>
+#include <cstdlib>
 
 #include "TError.h"
 #include "TRootSecContext.h"
diff --git a/net/auth/src/rsaaux.cxx b/net/auth/src/rsaaux.cxx
index a49f1736d9443..ea004b09896f8 100644
--- a/net/auth/src/rsaaux.cxx
+++ b/net/auth/src/rsaaux.cxx
@@ -29,11 +29,11 @@ MA  02110-1301  USA
 *                                                                               *
 *******************************************************************************/
 
-#include <stdio.h>
-#include <ctype.h>
-#include <string.h>
-#include <stdlib.h>
-#include <time.h>
+#include <cstdio>
+#include <cctype>
+#include <cstring>
+#include <cstdlib>
+#include <ctime>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
diff --git a/net/auth/src/rsalib.cxx b/net/auth/src/rsalib.cxx
index aad3b5e99f95b..e50aa79a6f250 100644
--- a/net/auth/src/rsalib.cxx
+++ b/net/auth/src/rsalib.cxx
@@ -29,11 +29,11 @@ MA  02110-1301  USA
 *                                                                              *
 *******************************************************************************/
 
-#include <stdio.h>
-#include <string.h>
-#include <ctype.h>
-#include <stdlib.h>
-#include <errno.h>
+#include <cstdio>
+#include <cstring>
+#include <cctype>
+#include <cstdlib>
+#include <cerrno>
 
 #include "rsaaux.h"
 #include "rsalib.h"
diff --git a/net/davix/src/TDavixFileInternal.h b/net/davix/src/TDavixFileInternal.h
index c2561c760f2ce..73b227e4db48f 100644
--- a/net/davix/src/TDavixFileInternal.h
+++ b/net/davix/src/TDavixFileInternal.h
@@ -18,8 +18,8 @@
 #include <vector>
 #include <iterator>
 #include <algorithm>
-#include <errno.h>
-#include <stdlib.h>
+#include <cerrno>
+#include <cstdlib>
 #include <unistd.h>
 #include <fcntl.h>
 #include <sys/stat.h>
diff --git a/net/davix/src/TDavixSystem.cxx b/net/davix/src/TDavixSystem.cxx
index 344d31bb73585..27fd65df58aae 100644
--- a/net/davix/src/TDavixSystem.cxx
+++ b/net/davix/src/TDavixSystem.cxx
@@ -35,8 +35,8 @@
 #include "TVirtualPerfStats.h"
 #include "TDavixFileInternal.h"
 
-#include <errno.h>
-#include <stdlib.h>
+#include <cerrno>
+#include <cstdlib>
 #include <unistd.h>
 #include <fcntl.h>
 #include <davix.hpp>
diff --git a/net/net/src/TApplicationRemote.cxx b/net/net/src/TApplicationRemote.cxx
index c7fd2913a67b4..c94e899bb25ec 100644
--- a/net/net/src/TApplicationRemote.cxx
+++ b/net/net/src/TApplicationRemote.cxx
@@ -20,7 +20,7 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include <errno.h>
+#include <cerrno>
 #include <random>
 
 #include "TApplicationRemote.h"
diff --git a/net/net/src/TFTP.cxx b/net/net/src/TFTP.cxx
index 454a67931ce03..3f2012ebf7391 100644
--- a/net/net/src/TFTP.cxx
+++ b/net/net/src/TFTP.cxx
@@ -22,7 +22,7 @@
 #include <ROOT/RConfig.hxx>
 
 #include <fcntl.h>
-#include <errno.h>
+#include <cerrno>
 #include <sys/stat.h>
 #ifndef R__WIN32
 #   include <unistd.h>
diff --git a/net/net/src/TNetFile.cxx b/net/net/src/TNetFile.cxx
index f5fb8bfa6e29c..01c4d4d29efd1 100644
--- a/net/net/src/TNetFile.cxx
+++ b/net/net/src/TNetFile.cxx
@@ -48,7 +48,7 @@ started either via inetd or by hand from the command line (no need
 to be super user).
 **/
 
-#include <errno.h>
+#include <cerrno>
 
 #include "Bytes.h"
 #include "NetErrors.h"
diff --git a/net/net/src/TS3HTTPRequest.cxx b/net/net/src/TS3HTTPRequest.cxx
index 7e79947794a20..dd49c537e4752 100644
--- a/net/net/src/TS3HTTPRequest.cxx
+++ b/net/net/src/TS3HTTPRequest.cxx
@@ -46,9 +46,9 @@
 #include <openssl/buffer.h>
 #endif
 
-#include <stdio.h>
-#include <time.h>
-#include <string.h>
+#include <cstdio>
+#include <ctime>
+#include <cstring>
 
 ClassImp(TS3HTTPRequest);
 
diff --git a/net/net/src/TWebFile.cxx b/net/net/src/TWebFile.cxx
index 248cd169f035f..dcbd7164a97dc 100644
--- a/net/net/src/TWebFile.cxx
+++ b/net/net/src/TWebFile.cxx
@@ -30,9 +30,9 @@
 #include "TSSLSocket.h"
 #endif
 
-#include <errno.h>
-#include <stdlib.h>
-#include <string.h>
+#include <cerrno>
+#include <cstdlib>
+#include <cstring>
 
 #ifdef WIN32
 # ifndef EADDRINUSE
diff --git a/net/rpdutils/src/DaemonUtils.cxx b/net/rpdutils/src/DaemonUtils.cxx
index d8b7e352e4d4c..d9b45699f5484 100644
--- a/net/rpdutils/src/DaemonUtils.cxx
+++ b/net/rpdutils/src/DaemonUtils.cxx
@@ -18,17 +18,17 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include <stdio.h>
-#include <string.h>
-#include <stdlib.h>
+#include <cstdio>
+#include <cstring>
+#include <cstdlib>
 #include <unistd.h>
-#include <signal.h>
+#include <csignal>
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <netinet/tcp.h>
 #include <arpa/inet.h>
 #include <netdb.h>
-#include <errno.h>
+#include <cerrno>
 
 #if defined(linux)
 #   include <features.h>
diff --git a/net/rpdutils/src/daemon.cxx b/net/rpdutils/src/daemon.cxx
index f43656f567829..c64b3d80f7045 100644
--- a/net/rpdutils/src/daemon.cxx
+++ b/net/rpdutils/src/daemon.cxx
@@ -18,10 +18,10 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include <stdio.h>
-#include <stdlib.h>
+#include <cstdio>
+#include <cstdlib>
 #include <unistd.h>
-#include <signal.h>
+#include <csignal>
 #include <sys/stat.h>
 #include <sys/param.h>
 #include <fcntl.h>
diff --git a/net/rpdutils/src/error.cxx b/net/rpdutils/src/error.cxx
index b13b25647e2a9..92e8f31b3a759 100644
--- a/net/rpdutils/src/error.cxx
+++ b/net/rpdutils/src/error.cxx
@@ -18,12 +18,12 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include <stdio.h>
+#include <cstdio>
 #include <unistd.h>
-#include <stdlib.h>
+#include <cstdlib>
 #include <syslog.h>
-#include <errno.h>
-#include <string.h>
+#include <cerrno>
+#include <cstring>
 #include "snprintf.h"
 
 #if defined(hpux9)
diff --git a/net/rpdutils/src/net.cxx b/net/rpdutils/src/net.cxx
index f7c184fc3e723..02f4c43b939a4 100644
--- a/net/rpdutils/src/net.cxx
+++ b/net/rpdutils/src/net.cxx
@@ -19,17 +19,17 @@
 
 #include <ROOT/RConfig.hxx>
 
-#include <stdio.h>
-#include <string.h>
-#include <stdlib.h>
+#include <cstdio>
+#include <cstring>
+#include <cstdlib>
 #include <unistd.h>
-#include <signal.h>
+#include <csignal>
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <netinet/tcp.h>
 #include <arpa/inet.h>
 #include <netdb.h>
-#include <errno.h>
+#include <cerrno>
 
 #include "rpdp.h"
 #include "rpderr.h"
diff --git a/net/rpdutils/src/netpar.cxx b/net/rpdutils/src/netpar.cxx
index a781ca965846a..465bcdf797972 100644
--- a/net/rpdutils/src/netpar.cxx
+++ b/net/rpdutils/src/netpar.cxx
@@ -21,18 +21,18 @@
 #include <ROOT/RConfig.hxx>
 
 // avoid warning due to wrong bzero prototype (used by FD_ZERO macro)
-#include <stdio.h>
-#include <string.h>
-#include <stdlib.h>
+#include <cstdio>
+#include <cstring>
+#include <cstdlib>
 #include <unistd.h>
-#include <signal.h>
+#include <csignal>
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <netinet/tcp.h>
 #include <arpa/inet.h>
 #include <netdb.h>
 #include <fcntl.h>
-#include <errno.h>
+#include <cerrno>
 #if defined(_AIX)
 #include <strings.h>
 #endif
diff --git a/net/rpdutils/src/rpdconn.cxx b/net/rpdutils/src/rpdconn.cxx
index e1009e50d4669..0eb8b9e85f63a 100644
--- a/net/rpdutils/src/rpdconn.cxx
+++ b/net/rpdutils/src/rpdconn.cxx
@@ -21,12 +21,12 @@
 #include "rpdconn.h"
 
 #include <arpa/inet.h>
-#include <errno.h>
+#include <cerrno>
 #include <netdb.h>
 #include <poll.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 #include <sys/socket.h>
 #include <sys/stat.h>
 #include <sys/types.h>
diff --git a/net/rpdutils/src/rpdpriv.cxx b/net/rpdutils/src/rpdpriv.cxx
index 34e4229595e86..8ca082792d22b 100644
--- a/net/rpdutils/src/rpdpriv.cxx
+++ b/net/rpdutils/src/rpdpriv.cxx
@@ -23,11 +23,11 @@
 #include "RConfigure.h"
 
 #if !defined(WINDOWS)
-#include <stdio.h>
-#include <string.h>
+#include <cstdio>
+#include <cstring>
 #include <unistd.h>
 #include <pwd.h>
-#include <errno.h>
+#include <cerrno>
 #include <iostream>
 using std::cout, std::endl;
 
diff --git a/net/rpdutils/src/rpdutils.cxx b/net/rpdutils/src/rpdutils.cxx
index f36b01180014c..8e5e73d541318 100644
--- a/net/rpdutils/src/rpdutils.cxx
+++ b/net/rpdutils/src/rpdutils.cxx
@@ -22,7 +22,7 @@
 #include <ROOT/RConfig.hxx>
 #include "strlcpy.h"
 
-#include <ctype.h>
+#include <cctype>
 #include <fcntl.h>
 #include <pwd.h>
 #include <cstdio>
@@ -53,7 +53,7 @@
     defined(__APPLE__) || defined(__MACH__) || defined(cygwingcc)
 #include <grp.h>
 #include <sys/types.h>
-#include <signal.h>
+#include <csignal>
 #endif
 
 #ifdef _AIX
diff --git a/roofit/roofit/test/vectorisedPDFs/testCompatMode.cxx b/roofit/roofit/test/vectorisedPDFs/testCompatMode.cxx
index cf9778bc2233e..ebff0331c9278 100644
--- a/roofit/roofit/test/vectorisedPDFs/testCompatMode.cxx
+++ b/roofit/roofit/test/vectorisedPDFs/testCompatMode.cxx
@@ -22,7 +22,7 @@
 #include "TMath.h"
 #include "RooRandom.h"
 #include "RooFormulaVar.h"
-#include <math.h>
+#include <cmath>
 
 using namespace std;
 
diff --git a/roottest/boost/config/compiler/borland.hpp b/roottest/boost/config/compiler/borland.hpp
index a989fd633b2b2..f16bb0b2a6483 100644
--- a/roottest/boost/config/compiler/borland.hpp
+++ b/roottest/boost/config/compiler/borland.hpp
@@ -75,7 +75,7 @@
 #     undef strcmp
 #  endif
    // fix broken errno declaration:
-#  include <errno.h>
+#  include <cerrno>
 #  ifndef errno
 #     define errno errno
 #  endif
@@ -209,7 +209,7 @@
 // <climits> is partly broken, some macros define symbols that are really in
 // namespace std, so you end up having to use illegal constructs like
 // std::DBL_MAX, as a fix we'll just include float.h and have done with:
-#include <float.h>
+#include <cfloat>
 #endif
 //
 // __int64:
diff --git a/roottest/boost/config/compiler/codegear.hpp b/roottest/boost/config/compiler/codegear.hpp
index f6dc4c02ba224..270d76ca0fdb8 100644
--- a/roottest/boost/config/compiler/codegear.hpp
+++ b/roottest/boost/config/compiler/codegear.hpp
@@ -66,7 +66,7 @@
 #     undef strcmp
 #  endif
    // fix broken errno declaration:
-#  include <errno.h>
+#  include <cerrno>
 #  ifndef errno
 #     define errno errno
 #  endif
diff --git a/roottest/boost/config/platform/aix.hpp b/roottest/boost/config/platform/aix.hpp
index 894ef42ce9199..6c9ccc06d5cf4 100644
--- a/roottest/boost/config/platform/aix.hpp
+++ b/roottest/boost/config/platform/aix.hpp
@@ -15,7 +15,7 @@
 #define BOOST_HAS_CLOCK_GETTIME
 
 // This needs support in "boost/cstdint.hpp" exactly like FreeBSD.
-// This platform has header named <inttypes.h> which includes all
+// This platform has header named <cinttypes> which includes all
 // the things needed.
 #define BOOST_HAS_STDINT_H
 
diff --git a/roottest/boost/config/platform/bsd.hpp b/roottest/boost/config/platform/bsd.hpp
index a0142978eb7dc..2d3bf74a84042 100644
--- a/roottest/boost/config/platform/bsd.hpp
+++ b/roottest/boost/config/platform/bsd.hpp
@@ -60,7 +60,7 @@
 #  define BOOST_NO_CWCHAR
 #endif
 //
-// The BSD <ctype.h> has macros only, no functions:
+// The BSD <cctype> has macros only, no functions:
 //
 #if !defined(__OpenBSD__) || defined(__DragonFly__)
 #  define BOOST_NO_CTYPE_FUNCTIONS
diff --git a/roottest/boost/config/platform/hpux.hpp b/roottest/boost/config/platform/hpux.hpp
index 19ce68e59731b..cff40db50265d 100644
--- a/roottest/boost/config/platform/hpux.hpp
+++ b/roottest/boost/config/platform/hpux.hpp
@@ -13,7 +13,7 @@
 
 #define BOOST_PLATFORM "HP-UX"
 
-// In principle, HP-UX has a nice <stdint.h> under the name <inttypes.h>
+// In principle, HP-UX has a nice <cstdint> under the name <cinttypes>
 // However, it has the following problem:
 // Use of UINT32_C(0) results in "0u l" for the preprocessed source
 // (verifyable with gcc 2.95.3)
diff --git a/roottest/boost/config/platform/linux.hpp b/roottest/boost/config/platform/linux.hpp
index 51ae13347cdcb..ad18cc8ad659f 100644
--- a/roottest/boost/config/platform/linux.hpp
+++ b/roottest/boost/config/platform/linux.hpp
@@ -14,12 +14,12 @@
 #include <cstdlib>
 
 //
-// <stdint.h> added to glibc 2.1.1
+// <cstdint> added to glibc 2.1.1
 // We can only test for 2.1 though:
 //
 #if defined(__GLIBC__) && ((__GLIBC__ > 2) || ((__GLIBC__ == 2) && (__GLIBC_MINOR__ >= 1)))
-   // <stdint.h> defines int64_t unconditionally, but <sys/types.h> defines
-   // int64_t only if __GNUC__.  Thus, assume a fully usable <stdint.h>
+   // <cstdint> defines int64_t unconditionally, but <sys/types.h> defines
+   // int64_t only if __GNUC__.  Thus, assume a fully usable <cstdint>
    // only when using GCC.
 #  if defined __GNUC__
 #    define BOOST_HAS_STDINT_H
@@ -72,7 +72,7 @@
 #ifndef __GNUC__
 //
 // if the compiler is not gcc we still need to be able to parse
-// the GNU system headers, some of which (mainly <stdint.h>)
+// the GNU system headers, some of which (mainly <cstdint>)
 // use GNU specific extensions:
 //
 #  ifndef __extension__
diff --git a/roottest/boost/config/posix_features.hpp b/roottest/boost/config/posix_features.hpp
index d12954797f961..e635c5b1d6be2 100644
--- a/roottest/boost/config/posix_features.hpp
+++ b/roottest/boost/config/posix_features.hpp
@@ -22,7 +22,7 @@
 #        define BOOST_HAS_NL_TYPES_H
 #     endif
 
-      // POSIX version 6 requires <stdint.h>
+      // POSIX version 6 requires <cstdint>
 #     if defined(_POSIX_VERSION) && (_POSIX_VERSION >= 200100)
 #        define BOOST_HAS_STDINT_H
 #     endif
@@ -32,7 +32,7 @@
 #        define BOOST_HAS_DIRENT_H
 #     endif
 
-      // POSIX version 3 requires <signal.h> to have sigaction:
+      // POSIX version 3 requires <csignal> to have sigaction:
 #     if defined(_POSIX_VERSION) && (_POSIX_VERSION >= 199506L)
 #        define BOOST_HAS_SIGACTION
 #     endif
diff --git a/roottest/boost/config/stdlib/msl.hpp b/roottest/boost/config/stdlib/msl.hpp
index 8185e351ea0c9..f9f840e258b57 100644
--- a/roottest/boost/config/stdlib/msl.hpp
+++ b/roottest/boost/config/stdlib/msl.hpp
@@ -25,7 +25,7 @@
 #  define BOOST_NO_STD_MESSAGES
 #endif
 
-// check C lib version for <stdint.h>
+// check C lib version for <cstdint>
 #include <cstddef>
 
 #if defined(__MSL__) && (__MSL__ >= 0x5000)
diff --git a/roottest/boost/config/stdlib/stlport.hpp b/roottest/boost/config/stdlib/stlport.hpp
index 85176a4d92124..525f8c440e961 100644
--- a/roottest/boost/config/stdlib/stlport.hpp
+++ b/roottest/boost/config/stdlib/stlport.hpp
@@ -149,10 +149,10 @@
 #  endif
 #elif defined(__BORLANDC__) && __BORLANDC__ < 0x560
 // STLport doesn't import std::abs correctly:
-#include <stdlib.h>
+#include <cstdlib>
 namespace std { using ::abs; }
 // and strcmp/strcpy don't get imported either ('cos they are macros)
-#include <string.h>
+#include <cstring>
 #ifdef strcpy
 #  undef strcpy
 #endif
diff --git a/roottest/boost/config/suffix.hpp b/roottest/boost/config/suffix.hpp
index 9cce6fd736578..776c38069c42a 100644
--- a/roottest/boost/config/suffix.hpp
+++ b/roottest/boost/config/suffix.hpp
@@ -47,14 +47,14 @@
 #endif
 
 //
-// look for long long by looking for the appropriate macros in <limits.h>.
+// look for long long by looking for the appropriate macros in <climits>.
 // Note that we use limits.h rather than climits for maximal portability,
 // remember that since these just declare a bunch of macros, there should be
 // no namespace issues from this.
 //
 #if !defined(BOOST_HAS_LONG_LONG) && !defined(BOOST_NO_LONG_LONG)                                              \
    && !defined(BOOST_MSVC) && !defined(__BORLANDC__)
-# include <limits.h>
+# include <climits>
 # if (defined(ULLONG_MAX) || defined(ULONG_LONG_MAX) || defined(ULONGLONG_MAX))
 #   define BOOST_HAS_LONG_LONG
 # else
@@ -289,7 +289,7 @@
 
 //
 // If the compiler claims to be C99 conformant, then it had better
-// have a <stdint.h>:
+// have a <cstdint>:
 //
 #  if defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901)
 #     define BOOST_HAS_STDINT_H
diff --git a/roottest/cling/function/refClasses.cxx b/roottest/cling/function/refClasses.cxx
index 31d43dfc25e6c..792f38e64a2a9 100644
--- a/roottest/cling/function/refClasses.cxx
+++ b/roottest/cling/function/refClasses.cxx
@@ -1,7 +1,7 @@
 #ifndef refClasses_cxx
 #define refClasses_cxx
 
-#include <stdio.h>
+#include <cstdio>
 #include "TString.h"
 
 class yy {
diff --git a/roottest/cling/other/runStaticDataMember.C b/roottest/cling/other/runStaticDataMember.C
index a99b101b3a2c0..13ab9a426f4c6 100644
--- a/roottest/cling/other/runStaticDataMember.C
+++ b/roottest/cling/other/runStaticDataMember.C
@@ -1,6 +1,6 @@
 #include "runStaticDataMember.h"
 
-#include <stdio.h>
+#include <cstdio>
 
 using namespace std;
 
diff --git a/roottest/cling/other/runsnprintfselect.C b/roottest/cling/other/runsnprintfselect.C
index 29fd9fe79f49b..dcdfc19b57be9 100644
--- a/roottest/cling/other/runsnprintfselect.C
+++ b/roottest/cling/other/runsnprintfselect.C
@@ -1,4 +1,4 @@
-#include <stdio.h> 
+#include <cstdio> 
 #include <iostream>
 using namespace std;
 
diff --git a/roottest/cling/parsing/runReadbool.C b/roottest/cling/parsing/runReadbool.C
index f067ba5ad635d..847a6bd3cc3b1 100644
--- a/roottest/cling/parsing/runReadbool.C
+++ b/roottest/cling/parsing/runReadbool.C
@@ -1,4 +1,4 @@
-#include <stdio.h>
+#include <cstdio>
 
 bool tester(int i, bool &b,int expected) {
    if (b!=expected) {
diff --git a/roottest/cling/template/typedef/cmspb_orig.C b/roottest/cling/template/typedef/cmspb_orig.C
index ed180812b6d4a..88eed39b2c5a0 100644
--- a/roottest/cling/template/typedef/cmspb_orig.C
+++ b/roottest/cling/template/typedef/cmspb_orig.C
@@ -334,7 +334,7 @@ typedef unsigned int  wint_t;
 /* A null pointer constant.  */
 
 
-/* in case <stdio.h> has defined it. */
+/* in case <cstdio> has defined it. */
 
 
 /* G++ *//* G++ */
diff --git a/roottest/cling/typedef/func.C b/roottest/cling/typedef/func.C
index 8b2924e8fae76..21eca0dbe8319 100644
--- a/roottest/cling/typedef/func.C
+++ b/roottest/cling/typedef/func.C
@@ -1,4 +1,4 @@
-#include <stdio.h>
+#include <cstdio>
 
 
 void func(int a) {
diff --git a/roottest/graphics/macros/graphs/timeonaxis.C b/roottest/graphics/macros/graphs/timeonaxis.C
index 5d099bab135ab..b6b1fd8480929 100644
--- a/roottest/graphics/macros/graphs/timeonaxis.C
+++ b/roottest/graphics/macros/graphs/timeonaxis.C
@@ -21,7 +21,7 @@
 ///
 /// \author Damir Buskulic
 
-#include <time.h>
+#include <ctime>
 
 void timeonaxis()
 {
diff --git a/roottest/root/io/bill01/Dict.h b/roottest/root/io/bill01/Dict.h
index 1e0c3a496b5ad..4389b1fc2d5f9 100644
--- a/roottest/root/io/bill01/Dict.h
+++ b/roottest/root/io/bill01/Dict.h
@@ -5,10 +5,10 @@
 #error Dict.h/C is only for compilation. Abort cint.
 #endif
 #include <stddef.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <math.h>
-#include <string.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cmath>
+#include <cstring>
 #define G__ANSIHEADER
 #define G__DICTIONARY
 #include "G__ci.h"
diff --git a/roottest/root/io/bill02/Dict.h b/roottest/root/io/bill02/Dict.h
index 8d3346b7db891..c59980e35a7c4 100644
--- a/roottest/root/io/bill02/Dict.h
+++ b/roottest/root/io/bill02/Dict.h
@@ -5,10 +5,10 @@
 #error Dict.h/C is only for compilation. Abort cint.
 #endif
 #include <stddef.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <math.h>
-#include <string.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cmath>
+#include <cstring>
 #define G__ANSIHEADER
 #define G__DICTIONARY
 #include "G__ci.h"
diff --git a/roottest/root/io/emulated/marker.h b/roottest/root/io/emulated/marker.h
index cb33da54edf3d..bd75698750b27 100644
--- a/roottest/root/io/emulated/marker.h
+++ b/roottest/root/io/emulated/marker.h
@@ -1,7 +1,7 @@
 #ifndef marker_h
 #define marker_h
 
-#include <stdio.h>
+#include <cstdio>
 #include "TString.h"
 
 class Marker
diff --git a/roottest/root/io/evolution/array/MyClass.cxx b/roottest/root/io/evolution/array/MyClass.cxx
index 5d0491c5707e2..657f0db196db8 100644
--- a/roottest/root/io/evolution/array/MyClass.cxx
+++ b/roottest/root/io/evolution/array/MyClass.cxx
@@ -3,7 +3,7 @@
 #endif
 
 #include "MyClass.h"
-#include <stdlib.h>
+#include <cstdlib>
 #include <Riostream.h>
 #include <TObject.h>
 
diff --git a/roottest/root/io/newClassDef/new/InheritMulti.h b/roottest/root/io/newClassDef/new/InheritMulti.h
index 6a06bf47a0532..8200ee71cde4b 100644
--- a/roottest/root/io/newClassDef/new/InheritMulti.h
+++ b/roottest/root/io/newClassDef/new/InheritMulti.h
@@ -2,7 +2,7 @@
 #define InheritMulti_H
 
 #include "TObject.h"
-#include <stdio.h>
+#include <cstdio>
 
 // Test for multi-inheritance objects.
 
diff --git a/roottest/root/io/newClassDef/new/t3.C b/roottest/root/io/newClassDef/new/t3.C
index 9768c7840a850..58cd190db5587 100644
--- a/roottest/root/io/newClassDef/new/t3.C
+++ b/roottest/root/io/newClassDef/new/t3.C
@@ -1,4 +1,4 @@
-#include <stdio.h>
+#include <cstdio>
 void t3()
 {
 double epsilon = 10e-7;
diff --git a/roottest/root/io/stdpair/pairEnumEvo.C b/roottest/root/io/stdpair/pairEnumEvo.C
index 2be174cbfed76..456c76a3a8376 100644
--- a/roottest/root/io/stdpair/pairEnumEvo.C
+++ b/roottest/root/io/stdpair/pairEnumEvo.C
@@ -1,7 +1,7 @@
 #include "TROOT.h"
 #include "TClass.h"
 #include "TFile.h"
-#include <stdlib.h>
+#include <cstdlib>
 #include "TSystem.h"
 #include "TVirtualCollectionProxy.h"
 #include "TError.h"
diff --git a/roottest/root/math/vdt/stressVdt.cxx b/roottest/root/math/vdt/stressVdt.cxx
index cd5c54fab14b9..5e07b0e36919b 100644
--- a/roottest/root/math/vdt/stressVdt.cxx
+++ b/roottest/root/math/vdt/stressVdt.cxx
@@ -2,7 +2,7 @@
 #include <vector>
 #include <iostream>
 #include <cmath> //for log2
-#include <assert.h>
+#include <cassert>
 #include <limits>
 #include <functional>
 #include <iostream>
diff --git a/roottest/root/meta/autoloading/TriggerTypeDefs.h b/roottest/root/meta/autoloading/TriggerTypeDefs.h
index fc5109e8c6b51..dc1b9d5f47230 100644
--- a/roottest/root/meta/autoloading/TriggerTypeDefs.h
+++ b/roottest/root/meta/autoloading/TriggerTypeDefs.h
@@ -13,7 +13,7 @@
  */
 
 #include <vector>
-#include <stdint.h>
+#include <cstdint>
 
 namespace trigger
 {
diff --git a/roottest/root/meta/complete.cpp b/roottest/root/meta/complete.cpp
index 5c792be7ec573..9ed7b3b05546f 100644
--- a/roottest/root/meta/complete.cpp
+++ b/roottest/root/meta/complete.cpp
@@ -1,6 +1,6 @@
 // By Oliver Freyermuth; see ROOT-7103
 
-#include <string.h>
+#include <cstring>
 #include <set>
 
 #include "TClass.h"
diff --git a/roottest/root/meta/evolution/execMissingCheckSum.cxx b/roottest/root/meta/evolution/execMissingCheckSum.cxx
index e5f64a50e3d70..cf1a7e156d216 100644
--- a/roottest/root/meta/evolution/execMissingCheckSum.cxx
+++ b/roottest/root/meta/evolution/execMissingCheckSum.cxx
@@ -8,7 +8,7 @@ class MyClass {
    Int_t fValue;
 };
 
-#include <stdint.h>
+#include <cstdint>
 #include <vector>
 
 struct HcalFlagHFDigiTimeParam {
diff --git a/roottest/root/meta/genreflex/ROOT-5768/PyCool.h b/roottest/root/meta/genreflex/ROOT-5768/PyCool.h
index 6ae793fbcea70..014215c887c95 100644
--- a/roottest/root/meta/genreflex/ROOT-5768/PyCool.h
+++ b/roottest/root/meta/genreflex/ROOT-5768/PyCool.h
@@ -41,7 +41,7 @@
 // See also SealBase/DebugAids.h:83 (NDEBUG is defined as 1 else problems)
 //#ifdef _WIN32
 //#define NDEBUG 1
-//#include <assert.h>
+//#include <cassert>
 //#endif
 
 // Disable compilation warning C4345 ('behavior change: an object of POD type
diff --git a/roottest/root/meta/method/execConstMethod.cxx b/roottest/root/meta/method/execConstMethod.cxx
index 5fcac1f5c0f4a..a32517464e237 100644
--- a/roottest/root/meta/method/execConstMethod.cxx
+++ b/roottest/root/meta/method/execConstMethod.cxx
@@ -1,4 +1,4 @@
-#include <stdio.h>
+#include <cstdio>
 
 class Holder {
    int fValue;
diff --git a/roottest/root/meta/method/execConstructor.cxx b/roottest/root/meta/method/execConstructor.cxx
index 3632af2040967..c86ec82a234b9 100644
--- a/roottest/root/meta/method/execConstructor.cxx
+++ b/roottest/root/meta/method/execConstructor.cxx
@@ -1,4 +1,4 @@
-#include <stdio.h>
+#include <cstdio>
 
 class Holder {
 public:
diff --git a/roottest/root/meta/method/execInlined.cxx b/roottest/root/meta/method/execInlined.cxx
index c971360d2e4a8..623713ac41640 100644
--- a/roottest/root/meta/method/execInlined.cxx
+++ b/roottest/root/meta/method/execInlined.cxx
@@ -1,4 +1,4 @@
-#include <stdio.h>
+#include <cstdio>
 
 class MyClass {
    int fValue;
diff --git a/roottest/root/meta/naming/execResolveTypedef.cxx b/roottest/root/meta/naming/execResolveTypedef.cxx
index 034021f561c09..772609171ce1d 100644
--- a/roottest/root/meta/naming/execResolveTypedef.cxx
+++ b/roottest/root/meta/naming/execResolveTypedef.cxx
@@ -1,4 +1,4 @@
-#include <stdio.h>
+#include <cstdio>
 #include <TClassEdit.h>
 #include <TClass.h>
 #include <cstdint>
diff --git a/roottest/root/meta/tclass/execTClassRehash.C b/roottest/root/meta/tclass/execTClassRehash.C
index 792017d87e16c..c2c03efc776c2 100644
--- a/roottest/root/meta/tclass/execTClassRehash.C
+++ b/roottest/root/meta/tclass/execTClassRehash.C
@@ -6,7 +6,7 @@
 #include "TString.h"
 #include "TSystem.h"
 
-#include <stdio.h>
+#include <cstdio>
 
 void LoadAllTClass()
 {
diff --git a/roottest/root/multicore/fork.cpp b/roottest/root/multicore/fork.cpp
index 5c6d085bd3d94..e0028db775c7f 100644
--- a/roottest/root/multicore/fork.cpp
+++ b/roottest/root/multicore/fork.cpp
@@ -1,4 +1,4 @@
-#include <stdio.h>
+#include <cstdio>
 #include <unistd.h>
 #include <fstream>
 #include <iostream>
diff --git a/roottest/root/multicore/generate_imt_tree.C b/roottest/root/multicore/generate_imt_tree.C
index 6c3154e152575..f72b731eaf105 100644
--- a/roottest/root/multicore/generate_imt_tree.C
+++ b/roottest/root/multicore/generate_imt_tree.C
@@ -4,7 +4,7 @@
 #include "TRandom.h"
 #include "TTree.h"
 
-#include <stdlib.h>
+#include <cstdlib>
 #include <iostream>
 #include <string>
 #include <vector>
diff --git a/roottest/root/selector/simple/testSelector.h b/roottest/root/selector/simple/testSelector.h
index 7fa429a6a65e4..bcf8d231a1b19 100644
--- a/roottest/root/selector/simple/testSelector.h
+++ b/roottest/root/selector/simple/testSelector.h
@@ -1,7 +1,7 @@
 #include "TSelector.h"
 #include "TDatime.h"
 #include "TH1.h"
-#include <stdio.h>
+#include <cstdio>
 
 class testSelector: public TSelector {
  public:
diff --git a/roottest/root/tree/addresses/runprova.C b/roottest/root/tree/addresses/runprova.C
index ee5e6b626d958..b498be94a96b0 100644
--- a/roottest/root/tree/addresses/runprova.C
+++ b/roottest/root/tree/addresses/runprova.C
@@ -1,6 +1,6 @@
 #include "TROOT.h"
 #include "TMinuit.h"
-#include <stdio.h>
+#include <cstdio>
 #include <fcntl.h>
 #include <iostream>
 #include <fstream>
diff --git a/roottest/root/tree/array/TestObj.h b/roottest/root/tree/array/TestObj.h
index a6babd2a86369..0d4e098e6dc54 100644
--- a/roottest/root/tree/array/TestObj.h
+++ b/roottest/root/tree/array/TestObj.h
@@ -8,7 +8,7 @@
 #include <TClass.h>
 #include <TClonesArray.h>
 
-#include <stdio.h>
+#include <cstdio>
 
 class Particle {
                 public:
diff --git a/roottest/root/tree/chain/execEmpty.C b/roottest/root/tree/chain/execEmpty.C
index 691ba22fd317e..72ad2561eb611 100644
--- a/roottest/root/tree/chain/execEmpty.C
+++ b/roottest/root/tree/chain/execEmpty.C
@@ -1,6 +1,6 @@
 #include "TObject.h"
 #include "TChain.h"
-#include <stdio.h>
+#include <cstdio>
 
 struct CallBack : public TObject {
   CallBack(TChain *ch) : fChain(ch) {};
diff --git a/roottest/root/tree/cloning/runtreeCloneTest2.C b/roottest/root/tree/cloning/runtreeCloneTest2.C
index cb8947b11409e..76ce153ddbb91 100644
--- a/roottest/root/tree/cloning/runtreeCloneTest2.C
+++ b/roottest/root/tree/cloning/runtreeCloneTest2.C
@@ -26,7 +26,7 @@ Use $ROOTSYS/bin/hadd to merge many histogram files
 */
 
 
-#include <string.h>
+#include <cstring>
 #include "TChain.h"
 #include "TFile.h"
 #include "TH1.h"
diff --git a/roottest/root/tree/entrylist/execTEntryListArray.cxx b/roottest/root/tree/entrylist/execTEntryListArray.cxx
index ec6d759fe7e1d..056757bfc1769 100644
--- a/roottest/root/tree/entrylist/execTEntryListArray.cxx
+++ b/roottest/root/tree/entrylist/execTEntryListArray.cxx
@@ -1,4 +1,4 @@
-#include <stdlib.h>
+#include <cstdlib>
 #include "TApplication.h"
 #include "TTree.h"
 #include "TChain.h"
diff --git a/roottest/root/tree/reader/runcleanupChain.C b/roottest/root/tree/reader/runcleanupChain.C
index edbd0a5d003a6..277f90bb8e4d7 100644
--- a/roottest/root/tree/reader/runcleanupChain.C
+++ b/roottest/root/tree/reader/runcleanupChain.C
@@ -2,7 +2,7 @@
 #include "TTreeReader.h"
 #include "TROOT.h"
 #include <vector>
-#include <stdio.h>
+#include <cstdio>
 
 Bool_t FindObject_loop(TCollection *col, TObject *obj)
 {
diff --git a/roottest/root/tree/selector/lhef_leg_sel.C b/roottest/root/tree/selector/lhef_leg_sel.C
index 57bbbaa1d0275..4ed10bc25ed19 100644
--- a/roottest/root/tree/selector/lhef_leg_sel.C
+++ b/roottest/root/tree/selector/lhef_leg_sel.C
@@ -1,5 +1,5 @@
 #include "lhef_leg_sel_gen.C"
-#include <stdio.h>
+#include <cstdio>
 
 class lhef_leg_sel : public lhef_leg_sel_gen {
    UInt_t nullValues = 0;
diff --git a/roottest/root/tree/selector/lhef_mc.C b/roottest/root/tree/selector/lhef_mc.C
index c94ee478478eb..fb3fdfa8e1deb 100644
--- a/roottest/root/tree/selector/lhef_mc.C
+++ b/roottest/root/tree/selector/lhef_mc.C
@@ -1,5 +1,5 @@
 #include "lhef_mc_gen.C"
-#include <stdio.h>
+#include <cstdio>
 
 class lhef_mc : public lhef_mc_gen {
    UInt_t nullValues = 0;
diff --git a/roottest/root/tree/selector/lhef_sel.C b/roottest/root/tree/selector/lhef_sel.C
index 4f8eb726abcbe..8d2d1fbc6616a 100644
--- a/roottest/root/tree/selector/lhef_sel.C
+++ b/roottest/root/tree/selector/lhef_sel.C
@@ -1,5 +1,5 @@
 #include "lhef_sel_gen.C"
-#include <stdio.h>
+#include <cstdio>
 
 class lhef_sel : public lhef_sel_gen {
    UInt_t nullValues = 0;
diff --git a/roottest/root/tree/selector/selabort.h b/roottest/root/tree/selector/selabort.h
index 8788accb2b807..e451071e0ef56 100644
--- a/roottest/root/tree/selector/selabort.h
+++ b/roottest/root/tree/selector/selabort.h
@@ -17,7 +17,7 @@
 #ifndef __CINT__
 #include <Riostream.h>
 #endif
-#include <stdio.h>
+#include <cstdio>
 
 class selabort : public TSelector {
    public :
diff --git a/roottest/root/treeformula/references/TreeFormulaReferencesGenerator.cxx b/roottest/root/treeformula/references/TreeFormulaReferencesGenerator.cxx
index 00a74b9f35afd..e86c71dbf75fd 100644
--- a/roottest/root/treeformula/references/TreeFormulaReferencesGenerator.cxx
+++ b/roottest/root/treeformula/references/TreeFormulaReferencesGenerator.cxx
@@ -80,7 +80,7 @@
 //
 ////////////////////////////////////////////////////////////////////////
 
-#include <stdlib.h>
+#include <cstdlib>
 
 #include "Riostream.h"
 #include "TROOT.h"
diff --git a/roottest/root/treeproxy/btagobjsScript.h b/roottest/root/treeproxy/btagobjsScript.h
index 10b222ccb506d..6cf936d51fff2 100644
--- a/roottest/root/treeproxy/btagobjsScript.h
+++ b/roottest/root/treeproxy/btagobjsScript.h
@@ -1,2 +1,2 @@
-#include <stdio.h>
+#include <cstdio>
 
diff --git a/roottest/root/treeproxy/vectorint/dude.h b/roottest/root/treeproxy/vectorint/dude.h
index 53c5fdf17996c..6f7a407812107 100644
--- a/roottest/root/treeproxy/vectorint/dude.h
+++ b/roottest/root/treeproxy/vectorint/dude.h
@@ -1 +1 @@
-#include <stdio.h>
+#include <cstdio>
diff --git a/roottest/scripts/analyze_valgrind.cxx b/roottest/scripts/analyze_valgrind.cxx
index 6a50188b7d136..071a4af89288b 100644
--- a/roottest/scripts/analyze_valgrind.cxx
+++ b/roottest/scripts/analyze_valgrind.cxx
@@ -5,7 +5,7 @@
 #include <set>
 #include <list>
 #include <sstream>
-#include <stdlib.h>
+#include <cstdlib>
 
 using namespace std;
 
diff --git a/sql/sqlite/src/TSQLiteStatement.cxx b/sql/sqlite/src/TSQLiteStatement.cxx
index 42a8c39709a5c..88c5cbf785eff 100644
--- a/sql/sqlite/src/TSQLiteStatement.cxx
+++ b/sql/sqlite/src/TSQLiteStatement.cxx
@@ -25,7 +25,7 @@
 
 #include <sqlite3.h>
 
-#include <stdlib.h>
+#include <cstdlib>
 
 ClassImp(TSQLiteStatement);
 
diff --git a/test/QpRandomDriver.cxx b/test/QpRandomDriver.cxx
index 68588137adba0..b7e820e672454 100644
--- a/test/QpRandomDriver.cxx
+++ b/test/QpRandomDriver.cxx
@@ -1,4 +1,4 @@
-#include <stdlib.h>
+#include <cstdlib>
 #include "Riostream.h"
 
 #include "TQpDataDens.h"
diff --git a/test/RootIDE/main.cxx b/test/RootIDE/main.cxx
index cf239d3c6fa00..c94c3a8adc148 100644
--- a/test/RootIDE/main.cxx
+++ b/test/RootIDE/main.cxx
@@ -9,7 +9,7 @@
  * For the list of contributors see $ROOTSYS/README/CREDITS.             *
  *************************************************************************/
 
-#include <stdio.h>
+#include <cstdio>
 
 #include <TSystem.h>
 #include <TApplication.h>
diff --git a/test/RootShower/MyParticle.cxx b/test/RootShower/MyParticle.cxx
index d4a0f54323ea7..916db8b4e17ae 100644
--- a/test/RootShower/MyParticle.cxx
+++ b/test/RootShower/MyParticle.cxx
@@ -7,7 +7,7 @@
  * For the licensing terms see the LICENSE file.                         *
  *************************************************************************/
 
-#include <stdlib.h>
+#include <cstdlib>
 
 #include <TSystem.h>
 #include <TRandom.h>
diff --git a/test/TFormulaParsingTests.h b/test/TFormulaParsingTests.h
index 131b7fa40a6b8..1b3ceb1d375aa 100644
--- a/test/TFormulaParsingTests.h
+++ b/test/TFormulaParsingTests.h
@@ -12,7 +12,7 @@
 
 #include <limits>
 #include <cstdlib>
-#include <stdio.h>
+#include <cstdio>
 // test of tformula neeeded to be run
 
 
diff --git a/test/TFormulaTests.cxx b/test/TFormulaTests.cxx
index 1aee24d8ef2a6..7df6e9da98ee4 100644
--- a/test/TFormulaTests.cxx
+++ b/test/TFormulaTests.cxx
@@ -1,7 +1,7 @@
 #include <cassert>
 #include <vector>
 #include <algorithm>
-#include <stdlib.h>
+#include <cstdlib>
 #include <TROOT.h>
 #include <TSystem.h>
 #include <TMath.h>
diff --git a/test/TestVectors.cxx b/test/TestVectors.cxx
index 7678eb1e53bb1..88e7d88b0fdde 100644
--- a/test/TestVectors.cxx
+++ b/test/TestVectors.cxx
@@ -8,7 +8,7 @@
 #include <TLorentzVector.h>
 #include <TRotation.h>
 #include <TLorentzRotation.h>
-#include <assert.h>
+#include <cassert>
 #endif
 
 Double_t DEPS=1.0e-14;
diff --git a/test/guitest.cxx b/test/guitest.cxx
index 2726a8f5b76be..c24728e753943 100644
--- a/test/guitest.cxx
+++ b/test/guitest.cxx
@@ -7,7 +7,7 @@
 // and slots communication mechanism can be found in $ROOTSYS/tutorials.
 // That version can be run entirely in the interpreter.
 
-#include <stdlib.h>
+#include <cstdlib>
 
 #include <TROOT.h>
 #include <TApplication.h>
diff --git a/test/minexam.cxx b/test/minexam.cxx
index 9f98e10b77c44..d922c03124804 100644
--- a/test/minexam.cxx
+++ b/test/minexam.cxx
@@ -28,8 +28,8 @@ int minexam();
 #include "TMath.h"
 #include "TStopwatch.h"
 
-#include <stdlib.h>
-#include <stdio.h>
+#include <cstdlib>
+#include <cstdio>
 
 ////////////////////////////////////////////////////////////////////////////////
 
diff --git a/test/rhtml/rhtml.cxx b/test/rhtml/rhtml.cxx
index 2911b4746c931..5d2ce6372d0ee 100644
--- a/test/rhtml/rhtml.cxx
+++ b/test/rhtml/rhtml.cxx
@@ -28,7 +28,7 @@
 #include "TSocket.h"
 #include "Riostream.h"
 #include "rhtml.h"
-#include <stdlib.h>
+#include <cstdlib>
 
 #ifdef WIN32
 #include "TWin32SplashThread.h"
diff --git a/test/stressEntryList.cxx b/test/stressEntryList.cxx
index 48b2a7f06301b..a08f24dc2772c 100644
--- a/test/stressEntryList.cxx
+++ b/test/stressEntryList.cxx
@@ -39,7 +39,7 @@
 #include <list>
 #include <array>
 #include <functional>
-#include <stdlib.h>
+#include <cstdlib>
 #include "TApplication.h"
 #include "TEntryList.h"
 #include "TEventList.h"
diff --git a/test/stressGraphics.cxx b/test/stressGraphics.cxx
index a5095fca4d4da..ab7c6fa7fe862 100644
--- a/test/stressGraphics.cxx
+++ b/test/stressGraphics.cxx
@@ -28,9 +28,9 @@
 //    root -b
 //    root [0] .x  stressGraphics.cxx
 
-#include <stdlib.h>
+#include <cstdlib>
 #include <Riostream.h>
-#include <time.h>
+#include <ctime>
 #include <string>
 #include <map>
 #include <vector>
diff --git a/test/stressInterpreter.cxx b/test/stressInterpreter.cxx
index 212acd47048cd..2b220fe049dd5 100644
--- a/test/stressInterpreter.cxx
+++ b/test/stressInterpreter.cxx
@@ -7,7 +7,7 @@
 //
 /////////////////////////////////////////////////////////////////
 
-#include <stdlib.h>
+#include <cstdlib>
 #include <iostream>
 #include <fstream>
 #include <vector>
diff --git a/test/stressVector.cxx b/test/stressVector.cxx
index 18dc97d421aa7..630bf8a0c93ef 100644
--- a/test/stressVector.cxx
+++ b/test/stressVector.cxx
@@ -35,7 +35,7 @@
 #include <iostream>
 #include <algorithm>
 
-#include <assert.h>
+#include <cassert>
 #include <map>
 
 #include "TStopwatch.h"
diff --git a/test/tcollex.cxx b/test/tcollex.cxx
index e039557d43545..919c41be98993 100644
--- a/test/tcollex.cxx
+++ b/test/tcollex.cxx
@@ -1,7 +1,7 @@
 // @(#)root/test:$Id$
 // Author: Fons Rademakers   19/08/96
 
-#include <stdlib.h>
+#include <cstdlib>
 
 #include "Riostream.h"
 #include "TString.h"
diff --git a/test/testbits.cxx b/test/testbits.cxx
index 27272e035451e..20d07832f0149 100644
--- a/test/testbits.cxx
+++ b/test/testbits.cxx
@@ -6,8 +6,8 @@
 #include "TROOT.h"
 #include "TBits.h"
 
-#include <stdlib.h>
-#include <stdio.h>
+#include <cstdlib>
+#include <cstdio>
 
 static const char *current_test;
 static unsigned test_count;
diff --git a/tmva/tmva/inc/TMVA/NeuralNet.h b/tmva/tmva/inc/TMVA/NeuralNet.h
index 256e32edcd00a..77d0c5203670c 100644
--- a/tmva/tmva/inc/TMVA/NeuralNet.h
+++ b/tmva/tmva/inc/TMVA/NeuralNet.h
@@ -49,7 +49,7 @@
 #include "TH1F.h"
 #include "TH2F.h"
 
-#include <fenv.h> // turn on or off exceptions for NaN and other numeric exceptions
+#include <cfenv> // turn on or off exceptions for NaN and other numeric exceptions
 
 
 namespace TMVA
diff --git a/tmva/tmva/src/BinarySearchTreeNode.cxx b/tmva/tmva/src/BinarySearchTreeNode.cxx
index 3cca37fae1ae8..4b414d206966b 100644
--- a/tmva/tmva/src/BinarySearchTreeNode.cxx
+++ b/tmva/tmva/src/BinarySearchTreeNode.cxx
@@ -40,7 +40,7 @@ the respective cut value.
 
 #include <stdexcept>
 #include <iomanip>
-#include <assert.h>
+#include <cassert>
 #include <cstdlib>
 
 #include "TString.h"
diff --git a/tmva/tmva/src/CCPruner.cxx b/tmva/tmva/src/CCPruner.cxx
index 4c5158dfa8821..2d4017ae2980d 100644
--- a/tmva/tmva/src/CCPruner.cxx
+++ b/tmva/tmva/src/CCPruner.cxx
@@ -31,7 +31,7 @@
 #include <iostream>
 #include <fstream>
 #include <limits>
-#include <math.h>
+#include <cmath>
 
 /*! \class TMVA::CCPruner
 \ingroup TMVA
diff --git a/tmva/tmva/src/ClassifierFactory.cxx b/tmva/tmva/src/ClassifierFactory.cxx
index 313845f4108af..20fef23ae2cbd 100644
--- a/tmva/tmva/src/ClassifierFactory.cxx
+++ b/tmva/tmva/src/ClassifierFactory.cxx
@@ -31,7 +31,7 @@ This is the MVA factory.
 #include "RtypesCore.h"
 #include "TString.h"
 
-#include <assert.h>
+#include <cassert>
 #include <iostream>
 
 class TString;
diff --git a/tmva/tmva/src/DNN/Architectures/Cpu/ActivationFunctions.hxx b/tmva/tmva/src/DNN/Architectures/Cpu/ActivationFunctions.hxx
index 0621a26b15985..052a1e7d2a497 100644
--- a/tmva/tmva/src/DNN/Architectures/Cpu/ActivationFunctions.hxx
+++ b/tmva/tmva/src/DNN/Architectures/Cpu/ActivationFunctions.hxx
@@ -15,7 +15,7 @@
  ///////////////////////////////////////////////////////////////////
 
 #include "TMVA/DNN/Architectures/Cpu.h"
-#include <math.h>
+#include <cmath>
 
 #ifdef R__HAS_VDT
 #include "vdt/tanh.h"
diff --git a/tmva/tmva/src/DNN/Architectures/Cuda/Propagation.cu b/tmva/tmva/src/DNN/Architectures/Cuda/Propagation.cu
index ce551a10d1c03..211ab9e678340 100644
--- a/tmva/tmva/src/DNN/Architectures/Cuda/Propagation.cu
+++ b/tmva/tmva/src/DNN/Architectures/Cuda/Propagation.cu
@@ -18,7 +18,7 @@
 #include "TMVA/DNN/Architectures/Cuda.h"
 #include "TMVA/DNN/Architectures/Cuda/Device.h"
 #include "Kernels.cuh"
-#include <math.h>
+#include <cmath>
 
 namespace TMVA {
 namespace DNN  {
diff --git a/tmva/tmva/src/DNN/Architectures/Cudnn/Propagate.cu b/tmva/tmva/src/DNN/Architectures/Cudnn/Propagate.cu
index 6d8be1c9dbb54..01616797675fb 100644
--- a/tmva/tmva/src/DNN/Architectures/Cudnn/Propagate.cu
+++ b/tmva/tmva/src/DNN/Architectures/Cudnn/Propagate.cu
@@ -25,7 +25,7 @@
 
 // #include "TMVA/DNN/Architectures/Cuda/Device.h"
 // #include "Kernels.cuh"*/
-// #include <math.h>
+// #include <cmath>
 
 // for std::numeric_limits<T>::max()
 #include <limits>
diff --git a/tmva/tmva/src/DNN/Architectures/Reference/ActivationFunctions.hxx b/tmva/tmva/src/DNN/Architectures/Reference/ActivationFunctions.hxx
index da74425b22953..d8e799826e696 100644
--- a/tmva/tmva/src/DNN/Architectures/Reference/ActivationFunctions.hxx
+++ b/tmva/tmva/src/DNN/Architectures/Reference/ActivationFunctions.hxx
@@ -15,7 +15,7 @@
  //////////////////////////////////////////////////////////////////
 
 #include "TMVA/DNN/Architectures/Reference.h"
-#include <math.h>
+#include <cmath>
 
 namespace TMVA
 {
diff --git a/tmva/tmva/src/DNN/Architectures/Reference/Arithmetic.hxx b/tmva/tmva/src/DNN/Architectures/Reference/Arithmetic.hxx
index 1af7d72ea306a..d77533721fec2 100644
--- a/tmva/tmva/src/DNN/Architectures/Reference/Arithmetic.hxx
+++ b/tmva/tmva/src/DNN/Architectures/Reference/Arithmetic.hxx
@@ -15,7 +15,7 @@
 //////////////////////////////////////////////////////////////////
 
 #include "TMVA/DNN/Architectures/Reference.h"
-#include <math.h>
+#include <cmath>
 
 namespace TMVA {
 namespace DNN {
diff --git a/tmva/tmva/src/DataSetFactory.cxx b/tmva/tmva/src/DataSetFactory.cxx
index 818a565472175..8b09d1bb9eb14 100644
--- a/tmva/tmva/src/DataSetFactory.cxx
+++ b/tmva/tmva/src/DataSetFactory.cxx
@@ -33,7 +33,7 @@ Class that contains all the data information
 
 */
 
-#include <assert.h>
+#include <cassert>
 
 #include <map>
 #include <vector>
diff --git a/tmva/tmva/src/MethodLikelihood.cxx b/tmva/tmva/src/MethodLikelihood.cxx
index 2e6db7a3b7d54..92031847b0496 100644
--- a/tmva/tmva/src/MethodLikelihood.cxx
+++ b/tmva/tmva/src/MethodLikelihood.cxx
@@ -783,7 +783,7 @@ void  TMVA::MethodLikelihood::WriteMonitoringHistosToFile( void ) const
 
 void TMVA::MethodLikelihood::MakeClassSpecificHeader( std::ostream& fout, const TString& ) const
 {
-   fout << "#include <math.h>" << std::endl;
+   fout << "#include <cmath>" << std::endl;
    fout << "#include <cstdlib>" << std::endl;
 }
 
diff --git a/tmva/tmva/src/ModulekNN.cxx b/tmva/tmva/src/ModulekNN.cxx
index b4b80695cd165..446a82da23afd 100644
--- a/tmva/tmva/src/ModulekNN.cxx
+++ b/tmva/tmva/src/ModulekNN.cxx
@@ -38,7 +38,7 @@
 #include "TMath.h"
 #include "TRandom3.h"
 
-#include <assert.h>
+#include <cassert>
 #include <iomanip>
 #include <iostream>
 #include <sstream>
diff --git a/tmva/tmva/src/RBDT.cxx b/tmva/tmva/src/RBDT.cxx
index 7c699c0aa999b..ca2858e15e201 100644
--- a/tmva/tmva/src/RBDT.cxx
+++ b/tmva/tmva/src/RBDT.cxx
@@ -28,7 +28,7 @@
 #include <iostream>
 #include <sstream>
 #include <stdexcept>
-#include <stdlib.h>
+#include <cstdlib>
 
 namespace {
 
diff --git a/tmva/tmva/test/DNN/TestCuda.cxx b/tmva/tmva/test/DNN/TestCuda.cxx
index 46c4597f979a7..f320fea9b7b82 100644
--- a/tmva/tmva/test/DNN/TestCuda.cxx
+++ b/tmva/tmva/test/DNN/TestCuda.cxx
@@ -1,7 +1,7 @@
 #include "Utility.h"
 #include "TMVA/DNN/Architectures/Cuda.h"
 #include "TMVA/DNN/Architectures/Reference.h"
-#include <stdlib.h>
+#include <cstdlib>
 
 using namespace TMVA::DNN;
 
diff --git a/tmva/tmva/test/DNN/TestCudnn.cxx b/tmva/tmva/test/DNN/TestCudnn.cxx
index 4dcb1949a3a1c..4418c95489a9f 100644
--- a/tmva/tmva/test/DNN/TestCudnn.cxx
+++ b/tmva/tmva/test/DNN/TestCudnn.cxx
@@ -1,7 +1,7 @@
 #include "Utility.h"
 #include "TMVA/DNN/Architectures/Cudnn.h"
 #include "TMVA/DNN/Architectures/Reference.h"
-#include <stdlib.h>
+#include <cstdlib>
 
 using namespace TMVA::DNN;
 
diff --git a/tmva/tmva/test/stressTMVA.cxx b/tmva/tmva/test/stressTMVA.cxx
index abee415bf4dc3..1e55de1729c08 100644
--- a/tmva/tmva/test/stressTMVA.cxx
+++ b/tmva/tmva/test/stressTMVA.cxx
@@ -3216,7 +3216,7 @@ void addComplexClassificationTests(UnitTestSuite &TMVA_test, bool full = true)
       new MethodUnitTestWithComplexData(trees, prep, TMVA::Types::kSVM, "SVM", "Gamma=0.4:Tol=0.001", 0.955, 0.975));
 }
 
-// #include <fenv.h>
+// #include <cfenv>
 
 int main(int argc, char **argv)
 {
diff --git a/tree/ntuple/src/RNTupleMerger.cxx b/tree/ntuple/src/RNTupleMerger.cxx
index c89375bf601fe..9b5462fbf2446 100644
--- a/tree/ntuple/src/RNTupleMerger.cxx
+++ b/tree/ntuple/src/RNTupleMerger.cxx
@@ -35,7 +35,7 @@
 
 #include <algorithm>
 #include <deque>
-#include <inttypes.h> // for PRIu64
+#include <cinttypes> // for PRIu64
 #include <initializer_list>
 #include <unordered_map>
 #include <vector>
diff --git a/tutorials/hist/hist061_TH1_timeonaxis.C b/tutorials/hist/hist061_TH1_timeonaxis.C
index 01c65ab3ee95f..01a847fdee4f0 100644
--- a/tutorials/hist/hist061_TH1_timeonaxis.C
+++ b/tutorials/hist/hist061_TH1_timeonaxis.C
@@ -21,7 +21,7 @@
 ///
 /// \author Damir Buskulic
 
-#include <time.h>
+#include <ctime>
 
 void hist061_TH1_timeonaxis()
 {
diff --git a/tutorials/io/hadd.C b/tutorials/io/hadd.C
index d6f250d4071cb..341937e9f3c29 100644
--- a/tutorials/io/hadd.C
+++ b/tutorials/io/hadd.C
@@ -17,7 +17,7 @@
 /// \author Sven A. Schmidt, sven.schmidt@cern.ch, 13.2.2001
 
 
-#include <string.h>
+#include <cstring>
 #include "TChain.h"
 #include "TFile.h"
 #include "TH1.h"
diff --git a/tutorials/math/r/GlobalMinimization.C b/tutorials/math/r/GlobalMinimization.C
index eb0a022012c8c..c8e4f4adc0608 100644
--- a/tutorials/math/r/GlobalMinimization.C
+++ b/tutorials/math/r/GlobalMinimization.C
@@ -11,8 +11,8 @@
 
 #include<TRInterface.h>
 #include<TBenchmark.h>
-#include<math.h>
-#include<stdlib.h>
+#include<cmath>
+#include<cstdlib>
 
 // In the next function the *double pointer should be changed by a TVectorD datatype,
 // because the pointer has no meaning in R's enviroment.
diff --git a/tutorials/roofit/roostats/rs_bernsteinCorrection.C b/tutorials/roofit/roostats/rs_bernsteinCorrection.C
index d0b200ed55029..6c0f38884c872 100644
--- a/tutorials/roofit/roostats/rs_bernsteinCorrection.C
+++ b/tutorials/roofit/roostats/rs_bernsteinCorrection.C
@@ -35,7 +35,7 @@
 #include "RooPlot.h"
 #include <string>
 #include <vector>
-#include <stdio.h>
+#include <cstdio>
 #include <sstream>
 #include <iostream>
 
diff --git a/tutorials/visualisation/eve/view3ds.C b/tutorials/visualisation/eve/view3ds.C
index d08cf5dad4a5b..c255ec1473a96 100644
--- a/tutorials/visualisation/eve/view3ds.C
+++ b/tutorials/visualisation/eve/view3ds.C
@@ -13,10 +13,10 @@
 #include "TStopwatch.h"
 #include "TError.h"
 
-#include <math.h>
-#include <stdlib.h>
-#include <stdio.h>
-#include <string.h>
+#include <cmath>
+#include <cstdlib>
+#include <cstdio>
+#include <cstring>
 
 class TEveTriangleSet;