diff --git a/FortranRuntime/lib/Runtime/stack.h → flang-rt/lib/flang_rt/stack.h b/FortranRuntime/lib/Runtime/stack.h → flang-rt/lib/flang_rt/stack.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/stack.h -------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/stack.h ------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -10,10 +10,10 @@
 // It is a list based stack with dynamic allocation/deallocation
 // of the list nodes.
 
-#ifndef FORTRAN_RUNTIME_STACK_H_
-#define FORTRAN_RUNTIME_STACK_H_
+#ifndef FORTRAN_FLANG_RT_STACK_H_
+#define FORTRAN_FLANG_RT_STACK_H_
 
-#include "FortranRuntime/Runtime/memory.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "terminator.h"
 
 namespace Fortran::runtime {
@@ -133,4 +133,4 @@ template <typename T, unsigned N = 0> class Stack : public StackStorage<T, N> {
   Terminator &terminator_;
 };
 } // namespace Fortran::runtime
-#endif /* FORTRAN_RUNTIME_STACK_H_ */
+#endif /* FORTRAN_FLANG_RT_STACK_H_ */
diff --git a/FortranRuntime/lib/Runtime/stat.cpp → flang-rt/lib/flang_rt/stat.cpp b/FortranRuntime/lib/Runtime/stat.cpp → flang-rt/lib/flang_rt/stat.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/stat.cpp ------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/stat.cpp -----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "stat.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "terminator.h"
 #include "tools.h"
 

diff --git a/FortranRuntime/lib/Runtime/stat.h → flang-rt/lib/flang_rt/stat.h b/FortranRuntime/lib/Runtime/stat.h → flang-rt/lib/flang_rt/stat.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/stat.h --------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/stat.h -------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -9,8 +9,8 @@
 // Defines the values returned by the runtime for STAT= specifiers
 // on executable statements.
 
-#ifndef FORTRAN_RUNTIME_STAT_H_
-#define FORTRAN_RUNTIME_STAT_H_
+#ifndef FORTRAN_FLANG_RT_STAT_H_
+#define FORTRAN_FLANG_RT_STAT_H_
 #include "flang/Common/ISO_Fortran_binding_wrapper.h"
 #include "flang/Common/api-attrs.h"
 #include "flang/Runtime/magic-numbers.h"
@@ -60,4 +60,4 @@ RT_API_ATTRS int ToErrmsg(const Descriptor *errmsg, int stat); // returns stat
 RT_API_ATTRS int ReturnError(Terminator &, int stat,
     const Descriptor *errmsg = nullptr, bool hasStat = false);
 } // namespace Fortran::runtime
-#endif /* FORTRAN_RUNTIME_STAT_H_ */
+#endif /* FORTRAN_FLANG_RT_STAT_H_ */
diff --git a/FortranRuntime/lib/Runtime/stop.cpp → flang-rt/lib/flang_rt/stop.cpp b/FortranRuntime/lib/Runtime/stop.cpp → flang-rt/lib/flang_rt/stop.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/stop.cpp ------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/stop.cpp -----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.

diff --git a/FortranRuntime/lib/Runtime/sum.cpp → flang-rt/lib/flang_rt/sum.cpp b/FortranRuntime/lib/Runtime/sum.cpp → flang-rt/lib/flang_rt/sum.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/sum.cpp -------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/sum.cpp ------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.

diff --git a/FortranRuntime/lib/Runtime/support.cpp → flang-rt/lib/flang_rt/support.cpp b/FortranRuntime/lib/Runtime/support.cpp → flang-rt/lib/flang_rt/support.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/support.cpp ---------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/support.cpp --------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,8 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/support.h"
-#include "FortranRuntime/Runtime/descriptor.h"
 #include "ISO_Fortran_util.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "type-info.h"
 
 namespace Fortran::runtime {

diff --git a/...anRuntime/lib/Runtime/temporary-stack.cpp → flang-rt/lib/flang_rt/temporary-stack.cpp b/...anRuntime/lib/Runtime/temporary-stack.cpp → flang-rt/lib/flang_rt/temporary-stack.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/temporary-stack.cpp -------------------------*- C++ -*-===//
+//===-- lib/flang_rt/temporary-stack.cpp ------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -10,8 +10,8 @@
 // temporaries. For use in HLFIR lowering.
 
 #include "flang/Runtime/temporary-stack.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/memory.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "terminator.h"
 #include "flang/Common/ISO_Fortran_binding_wrapper.h"
 #include "flang/Runtime/assign.h"

diff --git a/FortranRuntime/lib/Runtime/terminator.cpp → flang-rt/lib/flang_rt/terminator.cpp b/FortranRuntime/lib/Runtime/terminator.cpp → flang-rt/lib/flang_rt/terminator.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/terminator.cpp ------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/terminator.cpp -----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.

diff --git a/FortranRuntime/lib/Runtime/terminator.h → flang-rt/lib/flang_rt/terminator.h b/FortranRuntime/lib/Runtime/terminator.h → flang-rt/lib/flang_rt/terminator.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/terminator.h --------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/terminator.h -------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,8 +8,8 @@
 
 // Termination of the image
 
-#ifndef FORTRAN_RUNTIME_TERMINATOR_H_
-#define FORTRAN_RUNTIME_TERMINATOR_H_
+#ifndef FORTRAN_FLANG_RT_TERMINATOR_H_
+#define FORTRAN_FLANG_RT_TERMINATOR_H_
 
 #include "flang/Common/api-attrs.h"
 #include <cstdarg>
@@ -121,4 +121,4 @@ namespace Fortran::runtime::io {
 RT_API_ATTRS void FlushOutputOnCrash(const Terminator &);
 }
 
-#endif /* FORTRAN_RUNTIME_TERMINATOR_H_ */
+#endif /* FORTRAN_FLANG_RT_TERMINATOR_H_ */
diff --git a/...ranRuntime/lib/Runtime/time-intrinsic.cpp → flang-rt/lib/flang_rt/time-intrinsic.cpp b/...ranRuntime/lib/Runtime/time-intrinsic.cpp → flang-rt/lib/flang_rt/time-intrinsic.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/time-intrinsic.cpp --------------------------*- C++ -*-===//
+//===-- lib/flang_rt/time-intrinsic.cpp -------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -9,7 +9,7 @@
 // Implements time-related intrinsic subroutines.
 
 #include "flang/Runtime/time-intrinsic.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "terminator.h"
 #include "tools.h"
 #include "flang/Runtime/cpp-type.h"
@@ -62,7 +62,7 @@ template <typename Unused = void> double GetCpuTime(fallback_implementation) {
 
 #if defined __MINGW32__
 // clock_gettime is implemented in the pthread library for MinGW.
-// Using it here would mean that all programs that link libFortranRuntime are
+// Using it here would mean that all programs that link libflang_rt are
 // required to also link to pthread. Instead, don't use the function.
 #undef CLOCKID_CPU_TIME
 #undef CLOCKID_ELAPSED_TIME

diff --git a/FortranRuntime/lib/Runtime/tools.cpp → flang-rt/lib/flang_rt/tools.cpp b/FortranRuntime/lib/Runtime/tools.cpp → flang-rt/lib/flang_rt/tools.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/tools.cpp -----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/tools.cpp ----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.

diff --git a/FortranRuntime/lib/Runtime/tools.h → flang-rt/lib/flang_rt/tools.h b/FortranRuntime/lib/Runtime/tools.h → flang-rt/lib/flang_rt/tools.h
@@ -1,16 +1,16 @@
-//===-- lib/Runtime/tools.h -------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/tools.h ------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_TOOLS_H_
-#define FORTRAN_RUNTIME_TOOLS_H_
+#ifndef FORTRAN_FLANG_RT_TOOLS_H_
+#define FORTRAN_FLANG_RT_TOOLS_H_
 
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/memory.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "stat.h"
 #include "terminator.h"
 #include "flang/Common/optional.h"
@@ -535,4 +535,4 @@ RT_API_ATTRS void CreatePartialReductionResult(Descriptor &result,
     const char *intrinsic, TypeCode);
 
 } // namespace Fortran::runtime
-#endif /* FORTRAN_RUNTIME_TOOLS_H_ */
+#endif /* FORTRAN_FLANG_RT_TOOLS_H_ */
diff --git a/...nRuntime/lib/Runtime/transformational.cpp → flang-rt/lib/flang_rt/transformational.cpp b/...nRuntime/lib/Runtime/transformational.cpp → flang-rt/lib/flang_rt/transformational.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/transformational.cpp ------------------------*- C++ -*-===//
+//===-- lib/flang_rt/transformational.cpp -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -17,8 +17,8 @@
 // of the standard but it more likely to conform with its intent.
 
 #include "flang/Runtime/transformational.h"
-#include "FortranRuntime/Runtime/descriptor.h"
 #include "copy.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "terminator.h"
 #include "tools.h"
 #include "flang/Common/float128.h"

diff --git a/FortranRuntime/lib/Runtime/type-code.cpp → flang-rt/lib/flang_rt/type-code.cpp b/FortranRuntime/lib/Runtime/type-code.cpp → flang-rt/lib/flang_rt/type-code.cpp
@@ -1,12 +1,12 @@
-//===-- lib/Runtime/type-code.cpp -------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/type-code.cpp ------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include <cstdint>
 
 namespace Fortran::runtime {

diff --git a/FortranRuntime/lib/Runtime/type-info.cpp → flang-rt/lib/flang_rt/type-info.cpp b/FortranRuntime/lib/Runtime/type-info.cpp → flang-rt/lib/flang_rt/type-info.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/type-info.cpp -------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/type-info.cpp ------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.

diff --git a/FortranRuntime/lib/Runtime/type-info.h → flang-rt/lib/flang_rt/type-info.h b/FortranRuntime/lib/Runtime/type-info.h → flang-rt/lib/flang_rt/type-info.h
@@ -1,18 +1,18 @@
-//===-- lib/Runtime/type-info.h ---------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/type-info.h --------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_TYPE_INFO_H_
-#define FORTRAN_RUNTIME_TYPE_INFO_H_
+#ifndef FORTRAN_FLANG_RT_TYPE_INFO_H_
+#define FORTRAN_FLANG_RT_TYPE_INFO_H_
 
 // A C++ perspective of the derived type description schemata in
 // flang/module/__fortran_type_info.f90.
 
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "terminator.h"
 #include "flang/Common/Fortran-consts.h"
 #include "flang/Common/bit-population-count.h"
@@ -321,4 +321,4 @@ class DerivedType {
 };
 
 } // namespace Fortran::runtime::typeInfo
-#endif /* FORTRAN_RUNTIME_TYPE_INFO_H_ */
+#endif /* FORTRAN_FLANG_RT_TYPE_INFO_H_ */
diff --git a/FortranRuntime/lib/Runtime/unit-map.cpp → flang-rt/lib/flang_rt/unit-map.cpp b/FortranRuntime/lib/Runtime/unit-map.cpp → flang-rt/lib/flang_rt/unit-map.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/unit-map.cpp --------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/unit-map.cpp -------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.

diff --git a/FortranRuntime/lib/Runtime/unit-map.h → flang-rt/lib/flang_rt/unit-map.h b/FortranRuntime/lib/Runtime/unit-map.h → flang-rt/lib/flang_rt/unit-map.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/unit-map.h ----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/unit-map.h ---------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -9,10 +9,10 @@
 // Maps Fortran unit numbers to their ExternalFileUnit instances.
 // A simple hash table with forward-linked chains per bucket.
 
-#ifndef FORTRAN_RUNTIME_UNIT_MAP_H_
-#define FORTRAN_RUNTIME_UNIT_MAP_H_
+#ifndef FORTRAN_FLANG_RT_UNIT_MAP_H_
+#define FORTRAN_FLANG_RT_UNIT_MAP_H_
 
-#include "FortranRuntime/Runtime/memory.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "lock.h"
 #include "unit.h"
 #include "flang/Common/fast-int-set.h"
@@ -100,4 +100,4 @@ class UnitMap {
   int emergencyNewUnit_{maxNewUnits_}; // not recycled
 };
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_UNIT_MAP_H_ */
+#endif /* FORTRAN_FLANG_RT_UNIT_MAP_H_ */
diff --git a/FortranRuntime/lib/Runtime/unit.cpp → flang-rt/lib/flang_rt/unit.cpp b/FortranRuntime/lib/Runtime/unit.cpp → flang-rt/lib/flang_rt/unit.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/unit.cpp ------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/unit.cpp -----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -19,13 +19,13 @@
 
 namespace Fortran::runtime::io {
 
-#ifndef FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
+#ifndef FLANGRT_NO_GLOBAL_VAR_DEFS
 RT_OFFLOAD_VAR_GROUP_BEGIN
 RT_VAR_ATTRS ExternalFileUnit *defaultInput{nullptr}; // unit 5
 RT_VAR_ATTRS ExternalFileUnit *defaultOutput{nullptr}; // unit 6
 RT_VAR_ATTRS ExternalFileUnit *errorOutput{nullptr}; // unit 0 extension
 RT_OFFLOAD_VAR_GROUP_END
-#endif // FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
+#endif // FLANGRT_NO_GLOBAL_VAR_DEFS
 
 RT_OFFLOAD_API_GROUP_BEGIN
 

diff --git a/FortranRuntime/lib/Runtime/unit.h → flang-rt/lib/flang_rt/unit.h b/FortranRuntime/lib/Runtime/unit.h → flang-rt/lib/flang_rt/unit.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/unit.h --------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/unit.h -------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,14 +8,14 @@
 
 // Fortran external I/O units
 
-#ifndef FORTRAN_RUNTIME_UNIT_H_
-#define FORTRAN_RUNTIME_UNIT_H_
+#ifndef FORTRAN_FLANG_RT_UNIT_H_
+#define FORTRAN_FLANG_RT_UNIT_H_
 
-#include "FortranRuntime/Runtime/memory.h"
 #include "buffer.h"
 #include "connection.h"
 #include "environment.h"
 #include "file.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "format.h"
 #include "io-error.h"
 #include "io-stmt.h"
@@ -291,4 +291,4 @@ class ChildIo {
 };
 
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_UNIT_H_ */
+#endif /* FORTRAN_FLANG_RT_UNIT_H_ */
diff --git a/FortranRuntime/lib/Runtime/utf.cpp → flang-rt/lib/flang_rt/utf.cpp b/FortranRuntime/lib/Runtime/utf.cpp → flang-rt/lib/flang_rt/utf.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/utf.cpp -------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/utf.cpp ------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -10,7 +10,7 @@
 
 namespace Fortran::runtime {
 
-#ifndef FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
+#ifndef FLANGRT_NO_GLOBAL_VAR_DEFS
 // clang-format off
 RT_OFFLOAD_VAR_GROUP_BEGIN
 const RT_CONST_VAR_ATTRS std::uint8_t UTF8FirstByteTable[256]{
@@ -41,7 +41,7 @@ const RT_CONST_VAR_ATTRS std::uint8_t UTF8FirstByteTable[256]{
 };
 RT_OFFLOAD_VAR_GROUP_END
 // clang-format on
-#endif // FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
+#endif // FLANGRT_NO_GLOBAL_VAR_DEFS
 
 RT_OFFLOAD_API_GROUP_BEGIN
 

diff --git a/FortranRuntime/lib/Runtime/utf.h → flang-rt/lib/flang_rt/utf.h b/FortranRuntime/lib/Runtime/utf.h → flang-rt/lib/flang_rt/utf.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/utf.h ---------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/utf.h --------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -38,8 +38,8 @@
 // standard maximum.  However, we support extended forms up to 32 bits so that
 // CHARACTER(KIND=4) can be abused to hold arbitrary 32-bit data.
 
-#ifndef FORTRAN_RUNTIME_UTF_H_
-#define FORTRAN_RUNTIME_UTF_H_
+#ifndef FORTRAN_FLANG_RT_UTF_H_
+#define FORTRAN_FLANG_RT_UTF_H_
 
 #include "flang/Common/optional.h"
 #include <cstddef>
@@ -70,4 +70,4 @@ RT_API_ATTRS Fortran::common::optional<char32_t> DecodeUTF8(const char *);
 RT_API_ATTRS std::size_t EncodeUTF8(char *, char32_t);
 
 } // namespace Fortran::runtime
-#endif /* FORTRAN_RUNTIME_UTF_H_ */
+#endif /* FORTRAN_FLANG_RT_UTF_H_ */
diff --git a/FortranRuntime/test/CMakeLists.txt → flang-rt/test/CMakeLists.txt b/FortranRuntime/test/CMakeLists.txt → flang-rt/test/CMakeLists.txt
@@ -25,7 +25,7 @@ configure_lit_site_cfg(
   ${CMAKE_CURRENT_SOURCE_DIR}/lit.cfg.py
 )
 
-if (TARGET FortranRuntimeUnitTests)
+if (TARGET FlangRTUnitTests)
   configure_lit_site_cfg(
     ${CMAKE_CURRENT_SOURCE_DIR}/Unit/lit.site.cfg.py.in
     ${CMAKE_CURRENT_BINARY_DIR}/Unit/lit.site.cfg.py
@@ -41,29 +41,21 @@ if (TARGET FortranRuntimeUnitTests)
   )
 endif ()
 
-set(FORTRANRUNTIME_TEST_DEPENDS
-    FortranRuntimeUnitTests
-    FortranRuntime.static
+set(FLANGRT_TEST_DEPENDS
+    FlangRTUnitTests
+    flang_rt.unittest
   )
 
-add_custom_target(FortranRuntime-test-depends)
-set_target_properties(FortranRuntime-test-depends PROPERTIES FOLDER "Fortran Runtime/Meta")
-add_dependencies(FortranRuntime-test-depends ${FORTRANRUNTIME_TEST_DEPENDS})
+add_custom_target(flang-rt-test-depends)
+set_target_properties(flang-rt-test-depends PROPERTIES FOLDER "Fortran Runtime/Meta")
+add_dependencies(flang-rt-test-depends ${FLANGRT_TEST_DEPENDS})
 
-add_lit_testsuite(check-FortranRuntime "Running the FortranRuntime regression tests"
+add_lit_testsuite(check-flang-rt "Running the flang-rt regression tests"
   ${CMAKE_CURRENT_BINARY_DIR}
-  DEPENDS ${FORTRANRUNTIME_TEST_DEPENDS}
+  DEPENDS ${FLANGRT_TEST_DEPENDS}
 )
-set_target_properties(check-FortranRuntime PROPERTIES FOLDER "Fortran Runtime/Meta")
+set_target_properties(check-flang-rt PROPERTIES FOLDER "Fortran Runtime/Meta")
 
 
-add_lit_testsuites(FORTRANRUNTIME ${CMAKE_CURRENT_SOURCE_DIR}
-  DEPENDS ${FORTRANRUNTIME_TEST_DEPENDS})
-
-# To modify the default target triple for flang tests.
-if (DEFINED FLANG_TEST_TARGET_TRIPLE)
-  if (NOT DEFINED LLVM_TARGET_TRIPLE_ENV OR LLVM_TARGET_TRIPLE_ENV STREQUAL "")
-    message(FATAL_ERROR "LLVM_TARGET_TRIPLE_ENV must also be defined in order "
-                        "to use FLANG_TEST_TARGET_TRIPLE.")
-  endif()
-endif()
+add_lit_testsuites(flang-rt ${CMAKE_CURRENT_SOURCE_DIR}
+  DEPENDS ${FLANGRT_TEST_DEPENDS})
diff --git a/FortranRuntime/test/Driver/ctofortran.f90 → flang-rt/test/Driver/ctofortran.f90 b/FortranRuntime/test/Driver/ctofortran.f90 → flang-rt/test/Driver/ctofortran.f90
diff --git a/FortranRuntime/test/Driver/exec.f90 → flang-rt/test/Driver/exec.f90 b/FortranRuntime/test/Driver/exec.f90 → flang-rt/test/Driver/exec.f90
diff --git a/FortranRuntime/test/NonGtestUnit/lit.cfg.py → flang-rt/test/NonGtestUnit/lit.cfg.py b/FortranRuntime/test/NonGtestUnit/lit.cfg.py → flang-rt/test/NonGtestUnit/lit.cfg.py
@@ -5,18 +5,18 @@
 import lit.formats
 
 # name: The name of this test suite.
-config.name = "FortranRuntime-OldUnit"
+config.name = "flang-rt-OldUnit"
 
 # suffixes: A list of file extensions to treat as test files.
 # On Windows, ".exe" also matches the GTests and will execited redundantly.
 config.suffixes = [".test", ".exe"]
 
 # test_source_root: The root path where unit test binaries are located.
-config.test_source_root = os.path.join(config.fortranruntime_binary_dir, "unittests")
+config.test_source_root = os.path.join(config.flangrt_binary_dir, "unittests")
 
 # test_exec_root: The root path where tests should be run.
 # lit writes a '.lit_test_times.txt' file into this directory.
-config.test_exec_root = config.fortranruntime_binary_test_dir
+config.test_exec_root = config.flangrt_binary_test_dir
 
 # testFormat: The test format to use to interpret tests.
 config.test_format = lit.formats.ExecutableTest()
diff --git a/flang-rt/test/NonGtestUnit/lit.site.cfg.py.in b/flang-rt/test/NonGtestUnit/lit.site.cfg.py.in
@@ -0,0 +1,14 @@
+@LIT_SITE_CFG_IN_HEADER@
+
+import os
+
+config.llvm_tools_dir = "@LLVM_TOOLS_DIR@"
+config.flangrt_source_dir = "@FLANGRT_SOURCE_DIR@"
+config.flangrt_binary_dir = "@FLANGRT_BINARY_DIR@"
+config.flangrt_binary_test_dir = os.path.dirname(__file__)
+
+import lit.llvm
+lit.llvm.initialize(lit_config, config)
+
+# Let the main config do the real work.
+lit_config.load_config(config, os.path.join(config.flangrt_source_dir, 'test', 'NonGtestUnit', 'lit.cfg.py'))
diff --git a/FortranRuntime/test/Runtime/no-cpp-dep.c → flang-rt/test/Runtime/no-cpp-dep.c b/FortranRuntime/test/Runtime/no-cpp-dep.c → flang-rt/test/Runtime/no-cpp-dep.c
@@ -1,12 +1,12 @@
 /*
 This test makes sure that flang's runtime does not depend on the C++ runtime
-library. It tries to link this simple file against libFortranRuntime.a with
+library. It tries to link this simple file against libflang_rt.a with
 a C compiler.
 
 UNSUPPORTED: system-windows
 
-FIXME: This currently fails with CUDA-enabled FortranRuntime because it needs
-       to link libcuda_rt.
+FIXME: This currently fails with CUDA-enabled flang-rt because it needs
+       to link libcudart.
 
 RUN: %if system-aix %{ export OBJECT_MODE=64 %}
 RUN: %cc -std=c99 %s -I%include %libruntime -lm \

diff --git a/FortranRuntime/test/Unit/lit.cfg.py → flang-rt/test/Unit/lit.cfg.py b/FortranRuntime/test/Unit/lit.cfg.py → flang-rt/test/Unit/lit.cfg.py
@@ -5,17 +5,17 @@
 import lit.formats
 
 # name: The name of this test suite.
-config.name = "FortranRuntime-Unit"
+config.name = "flang-rt-Unit"
 
 # suffixes: A list of file extensions to treat as test files.
 config.suffixes = []
 
 # test_source_root: The root path where unit test binaries are located.
-config.test_source_root = os.path.join(config.fortranruntime_binary_dir, "unittests")
+config.test_source_root = os.path.join(config.flangrt_binary_dir, "unittests")
 
 # test_exec_root: The root path where tests should be run.
 # lit writes a '.lit_test_times.txt' file into this directory.
-config.test_exec_root = config.fortranruntime_binary_test_dir
+config.test_exec_root = config.flangrt_binary_test_dir
 
 # testFormat: The test format to use to interpret tests.
 config.test_format = lit.formats.GoogleTest(config.llvm_build_mode, "Tests")
diff --git a/flang-rt/test/Unit/lit.site.cfg.py.in b/flang-rt/test/Unit/lit.site.cfg.py.in
@@ -0,0 +1,15 @@
+@LIT_SITE_CFG_IN_HEADER@
+
+import os
+
+config.llvm_tools_dir = "@LLVM_TOOLS_DIR@"
+config.llvm_build_mode = "@LLVM_BUILD_MODE@"
+config.flangrt_source_dir = "@FLANGRT_SOURCE_DIR@"
+config.flangrt_binary_dir = "@FLANGRT_BINARY_DIR@"
+config.flangrt_binary_test_dir = os.path.dirname(__file__)
+
+import lit.llvm
+lit.llvm.initialize(lit_config, config)
+
+# Let the main config do the real work.
+lit_config.load_config(config, os.path.join(config.flangrt_source_dir, 'test', 'Unit', 'lit.cfg.py'))
diff --git a/FortranRuntime/test/lit.cfg.py → flang-rt/test/lit.cfg.py b/FortranRuntime/test/lit.cfg.py → flang-rt/test/lit.cfg.py
@@ -8,7 +8,7 @@
 # Configuration file for the 'lit' test runner.
 
 # name: The name of this test suite.
-config.name = "FortranRuntime"
+config.name = "flang-rt"
 
 # testFormat: The test format to use to interpret tests.
 #
@@ -54,7 +54,7 @@
 
 # test_exec_root: The root path where tests should be run.
 # lit writes a '.lit_test_times.txt' file into this directory.
-config.test_exec_root = config.fortranruntime_binary_test_dir
+config.test_exec_root = config.flangrt_binary_test_dir
 
 # On MacOS, -isysroot is needed to build binaries.
 isysroot_flag = []
@@ -72,15 +72,15 @@
 
 # Define some variables to help us test that the flang runtime doesn't depend on
 # the C++ runtime libraries. For this we need a C compiler.
-libruntime = os.path.join(config.fortranruntime_build_lib_dir, "libFortranRuntime.a")
+libruntime = os.path.join(config.flangrt_build_lib_dir, "libflang_rt.a")
 include = os.path.join(config.flang_source_dir, "include")
 tools.append(
     ToolSubst("%cc", command=config.cc, extra_args=isysroot_flag, unresolved="fatal")
 )
 tools.append(ToolSubst("%libruntime", command=libruntime, unresolved="fatal"))
 tools.append(ToolSubst("%include", command=include, unresolved="fatal"))
 
-# Lwt tests find LLVM's standard tools (FileCheck, split-file, not, ...)
+# Let tests find LLVM's standard tools (FileCheck, split-file, not, ...)
 llvm_config.with_environment("PATH", config.llvm_tools_dir, append_path=True)
 
 llvm_config.add_tool_substitutions(tools)
diff --git a/flang-rt/test/lit.site.cfg.py.in b/flang-rt/test/lit.site.cfg.py.in
@@ -0,0 +1,17 @@
+@LIT_SITE_CFG_IN_HEADER@
+
+import sys
+
+config.llvm_tools_dir = "@LLVM_TOOLS_DIR@"
+config.flang_source_dir = "@FLANG_SOURCE_DIR@"
+config.flangrt_source_dir = "@FLANGRT_SOURCE_DIR@"
+config.flangrt_binary_test_dir = os.path.dirname(__file__)
+config.flangrt_build_lib_dir = "@FLANGRT_BUILD_LIB_DIR@"
+config.cc = "@CMAKE_C_COMPILER@"
+config.osx_sysroot = path(r"@CMAKE_OSX_SYSROOT@")
+
+import lit.llvm
+lit.llvm.initialize(lit_config, config)
+
+# Let the main config do the real work.
+lit_config.load_config(config, os.path.join(config.flangrt_source_dir, 'test', 'lit.cfg.py'))
diff --git a/FortranRuntime/unittests/CMakeLists.txt → flang-rt/unittests/CMakeLists.txt b/FortranRuntime/unittests/CMakeLists.txt → flang-rt/unittests/CMakeLists.txt
@@ -26,13 +26,13 @@ endif()
 
 
 # Target that depends on all unittests
-add_custom_target(FortranRuntimeUnitTests)
-set_target_properties(FortranRuntimeUnitTests PROPERTIES FOLDER "Fortran Runtime/Meta")
+add_custom_target(FlangRTUnitTests)
+set_target_properties(FlangRTUnitTests PROPERTIES FOLDER "Fortran Runtime/Meta")
 
 
-function(add_fortranruntime_unittest_offload_properties target)
+function(add_flangrt_unittest_offload_properties target)
   # Set CUDA_RESOLVE_DEVICE_SYMBOLS.
-  if (FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT STREQUAL "CUDA")
+  if (FLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT STREQUAL "CUDA")
     set_target_properties(${target}
       PROPERTIES CUDA_RESOLVE_DEVICE_SYMBOLS ON
       )
@@ -43,7 +43,7 @@ function(add_fortranruntime_unittest_offload_properties target)
   #
   # FIXME: replace 'native' in --offload-arch option with the list
   #        of targets that Fortran Runtime was built for.
-  if (FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT STREQUAL "OpenMP")
+  if (FLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT STREQUAL "OpenMP")
     set_target_properties(${target}
       PROPERTIES LINK_OPTIONS
       "-fopenmp;--offload-arch=native"
@@ -52,22 +52,22 @@ function(add_fortranruntime_unittest_offload_properties target)
 endfunction()
 
 
-function(add_fortranruntime_unittest test_dirname)
+function(add_flangrt_unittest test_dirname)
   cmake_parse_arguments(ARG
     ""
     ""
     "LINK_LIBS"
     ${ARGN})
 
-  add_unittest(FortranRuntimeUnitTests ${test_dirname} ${ARG_UNPARSED_ARGUMENTS})
+  add_unittest(FlangRTUnitTests ${test_dirname} ${ARG_UNPARSED_ARGUMENTS})
 
-  target_include_directories(${test_dirname} PRIVATE "${FORTRANRUNTIME_SOURCE_DIR}/include")
+  target_include_directories(${test_dirname} PRIVATE "${FLANGRT_SOURCE_DIR}/include")
   target_include_directories(${test_dirname} PRIVATE "${FLANG_SOURCE_DIR}/include")
   target_link_libraries(${test_dirname} PRIVATE ${ARG_LINK_LIBS})
-  add_fortranruntime_unittest_offload_properties(${test_dirname})
+  add_flangrt_unittest_offload_properties(${test_dirname})
 endfunction()
 
-function(add_fortranruntime_nongtest_unittest test_name)
+function(add_flangrt_nongtest_unittest test_name)
   cmake_parse_arguments(ARG
     "SLOW_TEST"
     ""
@@ -83,15 +83,15 @@ function(add_fortranruntime_nongtest_unittest test_name)
   add_executable(${test_name}${suffix} ${ARG_UNPARSED_ARGUMENTS})
   set_target_properties(${test_name}${suffix} PROPERTIES FOLDER "Fortran Runtime/Tests/Unit")
 
-  target_include_directories(${test_name}${suffix} PRIVATE "${FORTRANRUNTIME_SOURCE_DIR}/include")
+  target_include_directories(${test_name}${suffix} PRIVATE "${FLANGRT_SOURCE_DIR}/include")
   target_include_directories(${test_name}${suffix} PRIVATE "${FLANG_SOURCE_DIR}/include")
   target_link_libraries(${test_name}${suffix} PRIVATE NonGTestTesting ${ARG_LINK_LIBS})
 
   if(NOT ARG_SLOW_TEST)
-    add_dependencies(FortranRuntimeUnitTests ${test_name}${suffix})
+    add_dependencies(FlangRTUnitTests ${test_name}${suffix})
   endif()
 
-  add_fortranruntime_unittest_offload_properties(${test_name}${suffix})
+  add_flangrt_unittest_offload_properties(${test_name}${suffix})
 endfunction()
 
 add_subdirectory(Evaluate)

diff --git a/...Runtime/unittests/Evaluate/CMakeLists.txt → flang-rt/unittests/Evaluate/CMakeLists.txt b/...Runtime/unittests/Evaluate/CMakeLists.txt → flang-rt/unittests/Evaluate/CMakeLists.txt
@@ -6,14 +6,14 @@
 #
 #===------------------------------------------------------------------------===#
 
-add_fortranruntime_nongtest_unittest(reshape
+add_flangrt_nongtest_unittest(reshape
   reshape.cpp
 LINK_LIBS
-  FortranRuntime.unittest
+  flang_rt.unittest
 )
 
-add_fortranruntime_nongtest_unittest(ISO-Fortran-binding
+add_flangrt_nongtest_unittest(ISO-Fortran-binding
   ISO-Fortran-binding.cpp
 LINK_LIBS
-  FortranRuntime.unittest
+  flang_rt.unittest
 )
diff --git a/...nittests/Evaluate/ISO-Fortran-binding.cpp → ...nittests/Evaluate/ISO-Fortran-binding.cpp b/...nittests/Evaluate/ISO-Fortran-binding.cpp → ...nittests/Evaluate/ISO-Fortran-binding.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "flang/Common/ISO_Fortran_binding_wrapper.h"
 #include "flang/Testing/testing.h"
 #include "llvm/Support/raw_ostream.h"

diff --git a/...ranRuntime/unittests/Evaluate/reshape.cpp → flang-rt/unittests/Evaluate/reshape.cpp b/...ranRuntime/unittests/Evaluate/reshape.cpp → flang-rt/unittests/Evaluate/reshape.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "flang/Runtime/transformational.h"
 #include "flang/Testing/testing.h"
 #include <cinttypes>

diff --git a/...nRuntime/unittests/Runtime/AccessTest.cpp → flang-rt/unittests/Runtime/AccessTest.cpp b/...nRuntime/unittests/Runtime/AccessTest.cpp → flang-rt/unittests/Runtime/AccessTest.cpp
diff --git a/...Runtime/unittests/Runtime/Allocatable.cpp → flang-rt/unittests/Runtime/Allocatable.cpp b/...Runtime/unittests/Runtime/Allocatable.cpp → flang-rt/unittests/Runtime/Allocatable.cpp
diff --git a/...me/unittests/Runtime/ArrayConstructor.cpp → ...rt/unittests/Runtime/ArrayConstructor.cpp b/...me/unittests/Runtime/ArrayConstructor.cpp → ...rt/unittests/Runtime/ArrayConstructor.cpp
@@ -6,9 +6,9 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/array-constructor.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/array-constructor.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 #include "flang/Runtime/allocatable.h"

diff --git a/...nRuntime/unittests/Runtime/BufferTest.cpp → flang-rt/unittests/Runtime/BufferTest.cpp b/...nRuntime/unittests/Runtime/BufferTest.cpp → flang-rt/unittests/Runtime/BufferTest.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "../../lib/Runtime/buffer.h"
+#include "../../lib/flang_rt/buffer.h"
 #include "CrashHandlerFixture.h"
 #include "gtest/gtest.h"
 #include <algorithm>

diff --git a/...nRuntime/unittests/Runtime/CMakeLists.txt → flang-rt/unittests/Runtime/CMakeLists.txt b/...nRuntime/unittests/Runtime/CMakeLists.txt → flang-rt/unittests/Runtime/CMakeLists.txt
@@ -6,7 +6,7 @@
 #
 #===------------------------------------------------------------------------===#
 
-add_fortranruntime_unittest(FlangRuntimeTests
+add_flangrt_unittest(RuntimeTests
   AccessTest.cpp
   Allocatable.cpp
   ArrayConstructor.cpp
@@ -38,9 +38,9 @@ add_fortranruntime_unittest(FlangRuntimeTests
   TemporaryStack.cpp
   Transformational.cpp
 LINK_LIBS
-  FortranRuntime.unittest
+  flang_rt.unittest
 )
 
-if (FORTRANRUNTIME_ENABLE_CUF)
+if (FLANG_RT_ENABLE_CUF)
   add_subdirectory(CUDA)
 endif ()
diff --git a/...e/unittests/Runtime/CUDA/AllocatorCUF.cpp → ...t/unittests/Runtime/CUDA/AllocatorCUF.cpp b/...e/unittests/Runtime/CUDA/AllocatorCUF.cpp → ...t/unittests/Runtime/CUDA/AllocatorCUF.cpp
@@ -6,16 +6,16 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/CUDA/allocator.h"
-#include "FortranRuntime/Runtime/CUDA/descriptor.h"
-#include "FortranRuntime/Runtime/allocatable.h"
-#include "FortranRuntime/Runtime/allocator-registry.h"
+#include "cuda_runtime.h"
+#include "flang-rt/flang_rt/allocator-registry.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "gtest/gtest.h"
-#include "../../../runtime/terminator.h"
+#include "../../../lib/flang_rt/terminator.h"
+#include "flang-rt/CufRuntime/allocator.h"
+#include "flang/Runtime/CUDA/descriptor.h"
+#include "flang/Runtime/allocatable.h"
 #include "flang/Support/Fortran.h"
 
-#include "cuda_runtime.h"
-
 using namespace Fortran::runtime;
 using namespace Fortran::runtime::cuda;
 

diff --git a/...ime/unittests/Runtime/CUDA/CMakeLists.txt → ...-rt/unittests/Runtime/CUDA/CMakeLists.txt b/...ime/unittests/Runtime/CUDA/CMakeLists.txt → ...-rt/unittests/Runtime/CUDA/CMakeLists.txt
@@ -6,14 +6,14 @@
 #
 #===------------------------------------------------------------------------===#
 
-add_fortranruntime_unittest(FlangCufRuntimeTests
+add_flangrt_unittest(FlangCufRuntimeTests
   AllocatorCUF.cpp
 )
 
 target_link_libraries(FlangCufRuntimeTests
   PRIVATE
   CufRuntime_cuda_${CUDAToolkit_VERSION_MAJOR}
-  FortranRuntime
+  flang_rt
 )
 
 target_include_directories(FlangCufRuntimeTests PRIVATE ${CUDAToolkit_INCLUDE_DIRS})
diff --git a/...ntime/unittests/Runtime/CharacterTest.cpp → flang-rt/unittests/Runtime/CharacterTest.cpp b/...ntime/unittests/Runtime/CharacterTest.cpp → flang-rt/unittests/Runtime/CharacterTest.cpp
@@ -10,7 +10,7 @@
 // in Fortran.
 
 #include "flang/Runtime/character.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "gtest/gtest.h"
 #include <cstring>
 #include <functional>

diff --git a/...Runtime/unittests/Runtime/CommandTest.cpp → flang-rt/unittests/Runtime/CommandTest.cpp b/...Runtime/unittests/Runtime/CommandTest.cpp → flang-rt/unittests/Runtime/CommandTest.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/command.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include "flang/Runtime/execute.h"

diff --git a/FortranRuntime/unittests/Runtime/Complex.cpp → flang-rt/unittests/Runtime/Complex.cpp b/FortranRuntime/unittests/Runtime/Complex.cpp → flang-rt/unittests/Runtime/Complex.cpp
diff --git a/...unittests/Runtime/CrashHandlerFixture.cpp → ...unittests/Runtime/CrashHandlerFixture.cpp b/...unittests/Runtime/CrashHandlerFixture.cpp → ...unittests/Runtime/CrashHandlerFixture.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 #include "CrashHandlerFixture.h"
-#include "../../lib/Runtime/terminator.h"
+#include "../../lib/flang_rt/terminator.h"
 #include <cstdarg>
 #include <cstdlib>
 

diff --git a/...e/unittests/Runtime/CrashHandlerFixture.h → ...t/unittests/Runtime/CrashHandlerFixture.h b/...e/unittests/Runtime/CrashHandlerFixture.h → ...t/unittests/Runtime/CrashHandlerFixture.h
diff --git a/FortranRuntime/unittests/Runtime/Derived.cpp → flang-rt/unittests/Runtime/Derived.cpp b/FortranRuntime/unittests/Runtime/Derived.cpp → flang-rt/unittests/Runtime/Derived.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 #include "flang/Runtime/derived-api.h"

diff --git a/...time/unittests/Runtime/ExternalIOTest.cpp → ...g-rt/unittests/Runtime/ExternalIOTest.cpp b/...time/unittests/Runtime/ExternalIOTest.cpp → ...g-rt/unittests/Runtime/ExternalIOTest.cpp
@@ -11,8 +11,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "CrashHandlerFixture.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/io-api-funcs.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/io-api-funcs.h"
 #include "gtest/gtest.h"
 #include "flang/Runtime/main.h"
 #include "flang/Runtime/stop.h"

diff --git a/FortranRuntime/unittests/Runtime/Format.cpp → flang-rt/unittests/Runtime/Format.cpp b/FortranRuntime/unittests/Runtime/Format.cpp → flang-rt/unittests/Runtime/Format.cpp
@@ -7,9 +7,9 @@
 //===----------------------------------------------------------------------===//
 
 #include "CrashHandlerFixture.h"
-#include "../../lib/Runtime/connection.h"
-#include "../../lib/Runtime/format-implementation.h"
-#include "../../lib/Runtime/io-error.h"
+#include "../../lib/flang_rt/connection.h"
+#include "../../lib/flang_rt/format-implementation.h"
+#include "../../lib/flang_rt/io-error.h"
 #include <optional>
 #include <string>
 #include <tuple>

diff --git a/FortranRuntime/unittests/Runtime/Inquiry.cpp → flang-rt/unittests/Runtime/Inquiry.cpp b/FortranRuntime/unittests/Runtime/Inquiry.cpp → flang-rt/unittests/Runtime/Inquiry.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/inquiry.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 

diff --git a/...ntime/unittests/Runtime/ListInputTest.cpp → flang-rt/unittests/Runtime/ListInputTest.cpp b/...ntime/unittests/Runtime/ListInputTest.cpp → flang-rt/unittests/Runtime/ListInputTest.cpp
@@ -7,9 +7,9 @@
 //===----------------------------------------------------------------------===//
 
 #include "CrashHandlerFixture.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/io-api-funcs.h"
-#include "../../lib/Runtime/io-error.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/io-api-funcs.h"
+#include "../../lib/flang_rt/io-error.h"
 
 using namespace Fortran::runtime;
 using namespace Fortran::runtime::io;

diff --git a/...e/unittests/Runtime/LogicalFormatTest.cpp → ...t/unittests/Runtime/LogicalFormatTest.cpp b/...e/unittests/Runtime/LogicalFormatTest.cpp → ...t/unittests/Runtime/LogicalFormatTest.cpp
@@ -7,8 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "CrashHandlerFixture.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/io-api-funcs.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/io-api-funcs.h"
 #include <algorithm>
 #include <array>
 #include <cstring>

diff --git a/FortranRuntime/unittests/Runtime/Matmul.cpp → flang-rt/unittests/Runtime/Matmul.cpp b/FortranRuntime/unittests/Runtime/Matmul.cpp → flang-rt/unittests/Runtime/Matmul.cpp
@@ -7,8 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/matmul.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 #include "flang/Runtime/allocatable.h"

diff --git a/...ime/unittests/Runtime/MatmulTranspose.cpp → ...-rt/unittests/Runtime/MatmulTranspose.cpp b/...ime/unittests/Runtime/MatmulTranspose.cpp → ...-rt/unittests/Runtime/MatmulTranspose.cpp
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 #include "flang/Runtime/allocatable.h"

diff --git a/...ntime/unittests/Runtime/MiscIntrinsic.cpp → flang-rt/unittests/Runtime/MiscIntrinsic.cpp b/...ntime/unittests/Runtime/MiscIntrinsic.cpp → flang-rt/unittests/Runtime/MiscIntrinsic.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 #include "flang/Runtime/allocatable.h"

diff --git a/...ranRuntime/unittests/Runtime/Namelist.cpp → flang-rt/unittests/Runtime/Namelist.cpp b/...ranRuntime/unittests/Runtime/Namelist.cpp → flang-rt/unittests/Runtime/Namelist.cpp
@@ -6,10 +6,10 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "../../lib/Runtime/namelist.h"
+#include "../../lib/flang_rt/namelist.h"
 #include "CrashHandlerFixture.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/io-api-funcs.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/io-api-funcs.h"
 #include "tools.h"
 #include <algorithm>
 #include <cinttypes>

diff --git a/FortranRuntime/unittests/Runtime/Numeric.cpp → flang-rt/unittests/Runtime/Numeric.cpp b/FortranRuntime/unittests/Runtime/Numeric.cpp → flang-rt/unittests/Runtime/Numeric.cpp
diff --git a/...unittests/Runtime/NumericalFormatTest.cpp → ...unittests/Runtime/NumericalFormatTest.cpp b/...unittests/Runtime/NumericalFormatTest.cpp → ...unittests/Runtime/NumericalFormatTest.cpp
@@ -7,8 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "CrashHandlerFixture.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/io-api-funcs.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/io-api-funcs.h"
 #include <algorithm>
 #include <array>
 #include <cstring>

diff --git a/FortranRuntime/unittests/Runtime/Pointer.cpp → flang-rt/unittests/Runtime/Pointer.cpp b/FortranRuntime/unittests/Runtime/Pointer.cpp → flang-rt/unittests/Runtime/Pointer.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/pointer.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 

diff --git a/FortranRuntime/unittests/Runtime/Ragged.cpp → flang-rt/unittests/Runtime/Ragged.cpp b/FortranRuntime/unittests/Runtime/Ragged.cpp → flang-rt/unittests/Runtime/Ragged.cpp
diff --git a/FortranRuntime/unittests/Runtime/Random.cpp → flang-rt/unittests/Runtime/Random.cpp b/FortranRuntime/unittests/Runtime/Random.cpp → flang-rt/unittests/Runtime/Random.cpp
@@ -7,8 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/random.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include <cmath>
 

diff --git a/...anRuntime/unittests/Runtime/Reduction.cpp → flang-rt/unittests/Runtime/Reduction.cpp b/...anRuntime/unittests/Runtime/Reduction.cpp → flang-rt/unittests/Runtime/Reduction.cpp
@@ -7,8 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/reduction.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 #include "flang/Common/float128.h"

diff --git a/...me/unittests/Runtime/RuntimeCrashTest.cpp → ...rt/unittests/Runtime/RuntimeCrashTest.cpp b/...me/unittests/Runtime/RuntimeCrashTest.cpp → ...rt/unittests/Runtime/RuntimeCrashTest.cpp
@@ -12,7 +12,7 @@
 //===----------------------------------------------------------------------===//
 #include "CrashHandlerFixture.h"
 #include "tools.h"
-#include "../../lib/Runtime/terminator.h"
+#include "../../lib/flang_rt/terminator.h"
 #include "flang/Runtime/io-api.h"
 #include "flang/Runtime/transformational.h"
 #include <gtest/gtest.h>

diff --git a/FortranRuntime/unittests/Runtime/Stop.cpp → flang-rt/unittests/Runtime/Stop.cpp b/FortranRuntime/unittests/Runtime/Stop.cpp → flang-rt/unittests/Runtime/Stop.cpp
@@ -11,7 +11,7 @@
 //===----------------------------------------------------------------------===//
 #include "flang/Runtime/stop.h"
 #include "CrashHandlerFixture.h"
-#include "../../lib/Runtime/environment.h"
+#include "../../lib/flang_rt/environment.h"
 #include <cstdlib>
 #include <gtest/gtest.h>
 

diff --git a/FortranRuntime/unittests/Runtime/Support.cpp → flang-rt/unittests/Runtime/Support.cpp b/FortranRuntime/unittests/Runtime/Support.cpp → flang-rt/unittests/Runtime/Support.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/support.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 

diff --git a/...time/unittests/Runtime/TemporaryStack.cpp → ...g-rt/unittests/Runtime/TemporaryStack.cpp b/...time/unittests/Runtime/TemporaryStack.cpp → ...g-rt/unittests/Runtime/TemporaryStack.cpp
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 #include "flang/Common/ISO_Fortran_binding_wrapper.h"

diff --git a/FortranRuntime/unittests/Runtime/Time.cpp → flang-rt/unittests/Runtime/Time.cpp b/FortranRuntime/unittests/Runtime/Time.cpp → flang-rt/unittests/Runtime/Time.cpp
diff --git a/...me/unittests/Runtime/Transformational.cpp → ...rt/unittests/Runtime/Transformational.cpp b/...me/unittests/Runtime/Transformational.cpp → ...rt/unittests/Runtime/Transformational.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/transformational.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 #include "flang/Common/float128.h"

diff --git a/FortranRuntime/unittests/Runtime/tools.h → flang-rt/unittests/Runtime/tools.h b/FortranRuntime/unittests/Runtime/tools.h → flang-rt/unittests/Runtime/tools.h
@@ -9,8 +9,8 @@
 #ifndef FORTRAN_UNITTESTS_RUNTIME_TOOLS_H_
 #define FORTRAN_UNITTESTS_RUNTIME_TOOLS_H_
 
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include "flang/Runtime/allocatable.h"
 #include "flang/Runtime/cpp-type.h"

diff --git a/flang/CMakeLists.txt b/flang/CMakeLists.txt
@@ -23,7 +23,6 @@ if (LLVM_ENABLE_EH)
 endif()
 
 set(FLANG_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
-set(FORTRANRUNTIME_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../FortranRuntime")
 
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR AND NOT MSVC_IDE)
   message(FATAL_ERROR "In-source builds are not allowed. \
@@ -247,13 +246,11 @@ set(LLVM_BUILD_TOOLS ON)
 
 include_directories(BEFORE
   ${FLANG_BINARY_DIR}/include
-  ${FLANG_SOURCE_DIR}/include
-  ${FORTRANRUNTIME_SOURCE_DIR}/include)
+  ${FLANG_SOURCE_DIR}/include)
 
 # Add Flang-centric modules to cmake path.
 list(INSERT CMAKE_MODULE_PATH 0
   "${FLANG_SOURCE_DIR}/cmake/modules"
-  "${FORTRANRUNTIME_SOURCE_DIR}/cmake/modules"
   "${LLVM_COMMON_CMAKE_UTILS}/Modules"
   )
 include(AddFlang)
@@ -271,7 +268,7 @@ set(FLANG_DEFAULT_LINKER "" CACHE STRING
   "Default linker to use (linker name or absolute path, empty for platform default)")
 
 set(FLANG_DEFAULT_RTLIB "" CACHE STRING
-   "Default Fortran runtime library to use (\"libFortranRuntime\"), leave empty for platform default.")
+   "Default Fortran runtime library to use (\"libflang_rt\"), leave empty for platform default.")
 
 if (NOT(FLANG_DEFAULT_RTLIB STREQUAL ""))
   message(WARNING "Resetting Flang's default runtime library to use platform default.")

diff --git a/...anRuntime/cmake/modules/FlangCommon.cmake → flang/cmake/modules/FlangCommon.cmake b/...anRuntime/cmake/modules/FlangCommon.cmake → flang/cmake/modules/FlangCommon.cmake
@@ -1,43 +1,43 @@
-#===-- cmake/modules/FlangCommon.txt ----------------------------===#
-#
-# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-# See https://llvm.org/LICENSE.txt for license information.
-# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-#
-#===------------------------------------------------------------------------===#
-#
-# CMake definitions shared betwween Flang and FortranRuntime
-#
-#===------------------------------------------------------------------------===#
-
-# The out of tree builds of the compiler and the Fortran runtime
-# must use the same setting of FLANG_RUNTIME_F128_MATH_LIB
-# to be composable. Failure to synchronize this setting may result
-# in linking errors or fatal failures in F128 runtime functions.
-set(FLANG_RUNTIME_F128_MATH_LIB "" CACHE STRING
-  "Specifies the target library used for implementing IEEE-754 128-bit float \
-  math in F18 runtime, e.g. it might be libquadmath for targets where \
-  REAL(16) is mapped to __float128, or libm for targets where REAL(16) \
-  is mapped to long double, etc."
-  )
-if (FLANG_RUNTIME_F128_MATH_LIB)
-  add_compile_definitions(FLANG_RUNTIME_F128_MATH_LIB="${FLANG_RUNTIME_F128_MATH_LIB}")
-endif()
-
-# Check if 128-bit float computations can be done via long double
-check_cxx_source_compiles(
-  "#include <cfloat>
-   #if LDBL_MANT_DIG != 113
-   #error LDBL_MANT_DIG != 113
-   #endif
-   int main() { return 0; }
-  "
-  HAVE_LDBL_MANT_DIG_113)
-
-include(TestBigEndian)
-test_big_endian(IS_BIGENDIAN)
-if (IS_BIGENDIAN)
-  add_compile_definitions(FLANG_BIG_ENDIAN=1)
-else ()
-  add_compile_definitions(FLANG_LITTLE_ENDIAN=1)
-endif ()
+#===-- cmake/modules/FlangCommon.txt ----------------------------===#
+#
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#
+#===------------------------------------------------------------------------===#
+#
+# CMake definitions shared between Flang and Flang-RT
+#
+#===------------------------------------------------------------------------===#
+
+# The out of tree builds of the compiler and the Fortran runtime
+# must use the same setting of FLANG_RUNTIME_F128_MATH_LIB
+# to be composable. Failure to synchronize this setting may result
+# in linking errors or fatal failures in F128 runtime functions.
+set(FLANG_RUNTIME_F128_MATH_LIB "" CACHE STRING
+  "Specifies the target library used for implementing IEEE-754 128-bit float \
+  math in F18 runtime, e.g. it might be libquadmath for targets where \
+  REAL(16) is mapped to __float128, or libm for targets where REAL(16) \
+  is mapped to long double, etc."
+  )
+if (FLANG_RUNTIME_F128_MATH_LIB)
+  add_compile_definitions(FLANG_RUNTIME_F128_MATH_LIB="${FLANG_RUNTIME_F128_MATH_LIB}")
+endif()
+
+# Check if 128-bit float computations can be done via long double
+check_cxx_source_compiles(
+  "#include <cfloat>
+   #if LDBL_MANT_DIG != 113
+   #error LDBL_MANT_DIG != 113
+   #endif
+   int main() { return 0; }
+  "
+  HAVE_LDBL_MANT_DIG_113)
+
+include(TestBigEndian)
+test_big_endian(IS_BIGENDIAN)
+if (IS_BIGENDIAN)
+  add_compile_definitions(FLANG_BIG_ENDIAN=1)
+else ()
+  add_compile_definitions(FLANG_LITTLE_ENDIAN=1)
+endif ()
diff --git a/flang/docs/FlangDriver.md b/flang/docs/FlangDriver.md
@@ -179,18 +179,18 @@ like this:
 
 ```
 $ flang -v -o example example.o
-"/usr/bin/ld" [...] example.o [...] "-lFortranRuntime" [...]
+"/usr/bin/ld" [...] example.o [...] "-lflang_rt" [...]
 ```
 
 The automatically added libraries are:
 
-* `FortranRuntime`: Provides most of the Flang runtime library.
+* `flang_rt`: Provides most of the Flang runtime library.
 
 If the code is C/C++ based and invokes Fortran routines, one can either use Clang
 or Flang as the linker driver.  If Clang is used, it will automatically all
 required runtime libraries needed by C++ (e.g., for STL) to the linker invocation.
-In this case, one has to explicitly provide the Fortran runtime libraries
-`FortranRuntime`.  An alternative is to use Flang to link.
+In this case, one has to explicitly provide the Fortran runtime library
+`flang_ty`.  An alternative is to use Flang to link.
 In this case, it may be required to explicitly supply C++ runtime libraries.
 
 On Darwin, the logical root where the system libraries are located (sysroot)

diff --git a/flang/docs/GettingStarted.md b/flang/docs/GettingStarted.md
@@ -32,8 +32,8 @@ tool.
 
 ### Building flang in tree (bootstrap build)
 Building flang in tree means building flang along with all of the projects on
-which it depends.  These projects include mlir, clang, flang, openmp,
-compiler-rt, and FortranRuntime.  Note that compiler-rt is only needed to access libraries that
+which it depends.  These projects include mlir, clang, flang, openmp, and
+compiler-rt.  Note that compiler-rt is only needed to access libraries that
 support 16 bit floating point numbers.  It's not needed to run the automated
 tests.  You can use several different C++ compilers for most of the build,
 includig GNU and clang.  But building compiler-rt requres using the clang
@@ -82,7 +82,7 @@ cmake \
   -DLLVM_TARGETS_TO_BUILD=host \
   -DLLVM_LIT_ARGS=-v \
   -DLLVM_ENABLE_PROJECTS="clang;mlir;flang;openmp" \
-  -DLLVM_ENABLE_RUNTIMES="compiler-rt;FortranRuntime" \
+  -DLLVM_ENABLE_RUNTIMES="compiler-rt;flang_rt" \
   ../llvm-project/llvm
 
 ninja
@@ -209,15 +209,15 @@ mkdir build_flang_runtime
 cd build_flang_runtime
 
 cmake \
-  -DLLVM_ENABLE_RUNTIMES=FortranRuntime \
-  -DFORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA \
+  -DLLVM_ENABLE_RUNTIMES=flang_rt \
+  -DFLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA \
   -DCMAKE_CUDA_ARCHITECTURES=80 \
   -DCMAKE_C_COMPILER=clang \
   -DCMAKE_CXX_COMPILER=clang++ \
   -DCMAKE_CUDA_COMPILER=clang \
   -DCMAKE_CUDA_HOST_COMPILER=clang++ \
   ../runtimes/
-make -j`nprocs` FortranRuntime
+make -j`nprocs` flang_rt
 ```
 
 Note that the used version of `clang` must [support](https://releases.llvm.org/16.0.0/tools/clang/docs/ReleaseNotes.html#cuda-support)
@@ -232,16 +232,16 @@ mkdir build_flang_runtime
 cd build_flang_runtime
 
 cmake \
-  -DLLVM_ENABLE_RUNTIMES=FortranRuntime \
-  -DFORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA \
+  -DLLVM_ENABLE_RUNTIMES=flang_rt \
+  -DFLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA \
   -DCMAKE_CUDA_ARCHITECTURES=80 \
   -DCMAKE_C_COMPILER=clang \
   -DCMAKE_CXX_COMPILER=clang++ \
   -DCMAKE_CUDA_COMPILER=nvcc \
   -DCMAKE_CUDA_HOST_COMPILER=clang++ \
   ../runtimes/
 
-make -j`nprocs` FortranRuntime
+make -j`nprocs` flang_rt
 ```
 
 Note that `nvcc` might limit support to certain
@@ -260,8 +260,8 @@ build config:
 
 For example:
 ```bash
-  -DLLVM_ENABLE_RUNTIMES=FortranRuntime \
-  -DFORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA \
+  -DLLVM_ENABLE_RUNTIMES=flang_rt \
+  -DFLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA \
   -DCMAKE_CUDA_ARCHITECTURES=80 \
   -DCMAKE_C_COMPILER=clang \
   -DCMAKE_CXX_COMPILER=clang++ \
@@ -272,8 +272,8 @@ For example:
 
 Or:
 ```bash
-  -DLLVM_ENABLE_RUNTIMES=FortranRuntime \
-  -DFORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA \
+  -DLLVM_ENABLE_RUNTIMES=flang_rt \
+  -DFLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA \
   -DCMAKE_CUDA_ARCHITECTURES=80 \
   -DCMAKE_C_COMPILER=gcc \
   -DCMAKE_CXX_COMPILER=g++ \
@@ -295,14 +295,14 @@ mkdir build_flang_runtime
 cd build_flang_runtime
 
 cmake \
-  -DLLVM_ENABLE_RUNTIMES=FortranRuntime \
-  -DFORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT="OpenMP" \
+  -DLLVM_ENABLE_RUNTIMES=flang_rt \
+  -DFLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT="OpenMP" \
   -DCMAKE_C_COMPILER=clang \
   -DCMAKE_CXX_COMPILER=clang++ \
-  -DFORTRANRUNTIME_DEVICE_ARCHITECTURES="all" \
+  -DFLANG_RT_DEVICE_ARCHITECTURES="all" \
   ../runtimes/
 
-make -j`nprocs` FortranRuntime
+make -j`nprocs` flang_rt
 ```
 
 The result of the build is a "device-only" library, i.e. the host

diff --git a/flang/docs/OpenACC-descriptor-management.md b/flang/docs/OpenACC-descriptor-management.md
@@ -427,7 +427,7 @@ The implementation's behavior may be described as (OpenACC 2.7.2):
 
 All the "is-present" checks and the data actions for the auxiliary pointers must be performed atomically with regards to the present counters bookkeeping.
 
-The API relies on the primitives provided by `liboffload`, so it is provided by a new F18 runtime library, e.g. `FortranOffloadRuntime`, that depends on `FortranRuntime` and `liboffload`.  The F18 driver adds `FortranOffloadRuntime` for linking under `-fopenacc`/`-fopenmp` (and maybe additional switches like `-fopenmp-targets`).
+The API relies on the primitives provided by `liboffload`, so it is provided by a new F18 runtime library, e.g. `FortranOffloadRuntime`, that depends on `flang_rt` and `liboffload`.  The F18 driver adds `FortranOffloadRuntime` for linking under `-fopenacc`/`-fopenmp` (and maybe additional switches like `-fopenmp-targets`).
 
 ## TODOs:
 

diff --git a/flang/docs/ReleaseNotes.md b/flang/docs/ReleaseNotes.md
@@ -36,12 +36,13 @@ page](https://llvm.org/releases/).
 
 ## Build System Changes
 
- * The Fortran Runtime library (libFortranRuntime) has been move to a new
-   top-level directory named "FortranRuntime". It now supports the
-   LLVM_ENABLE_RUNTIMES mechanism to build libFortranRuntime for multiple target
-   triples. libFortranRuntime.a will now be emitted into Clang's per-target
-   resource directory (next to libclang_rt) where it is also found by Flang's
-   driver.
+ * The Fortran Runtime library has been move to a new top-level directory
+   named "flang-rt". The library was also renamed from `libFortranRuntime.a` to
+   `libflang_rt.a`. It now supports the
+   LLVM_ENABLE_RUNTIMES mechanism to build flang-rt for multiple target
+   triples. libflang_rt.a will now be emitted into Clang's per-target
+   resource directory (next to libclang_rt.*.*) where it is also found by
+   Flang's driver.
 
 ## New Issues Found
 

diff --git a/flang/examples/ExternalHelloWorld/CMakeLists.txt b/flang/examples/ExternalHelloWorld/CMakeLists.txt
@@ -5,5 +5,5 @@ add_llvm_example(external-hello-world
 
 target_link_libraries(external-hello-world
   PRIVATE
-  FortranRuntime
+  flang_rt
   )
diff --git a/flang/include/flang/Common/README.md b/flang/include/flang/Common/README.md
@@ -1,8 +1,8 @@
-Files in this directory are used by Flang (the compiler) and FortranRuntime
+Files in this directory are used by Flang (the compiler) and flang-rt
 (the runtime library for Flang-compiled programs). They must be compatible by
 both. For definitions used only by Flang, consider
 `flang/{lib,include/flang}/Support` instead. For definitions used only by
-FortranRuntime, consider `FortranRuntime/{lib,include/FortranRuntime}/Runtime`.
+the runtime, consider `flang-rt/{lib,include/flang-rt}/flang_rt`.
 
 The requirements for common code include:
 
@@ -23,3 +23,5 @@ The requirements for common code include:
 
  * Global declarations may need to be annotated using definitions from
    `api-attrs.h`.
+
+ * The `Runtime` component is header-only.
diff --git a/flang/include/flang/ISO_Fortran_binding.h b/flang/include/flang/ISO_Fortran_binding.h
@@ -1,3 +1,11 @@
+//===-- include/flang/ISO_Fortran_binding.h ---------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
 /*===-- include/flang/ISO_Fortran_binding.h -----------------------*- C++ -*-===
  *
  * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
@@ -7,14 +15,14 @@
  * ===-----------------------------------------------------------------------===
  */
 
-#ifndef CFI_ISO_FORTRAN_BINDING_H_
-#define CFI_ISO_FORTRAN_BINDING_H_
+#ifndef FORTRAN_ISO_FORTRAN_BINDING_H_
+#define FORTRAN_ISO_FORTRAN_BINDING_H_
 
 /* When this header is included into the compiler and runtime implementations,
  * it does so by means of a wrapper header that establishes namespaces and
  * a macro for extra function attributes (RT_API_ATTRS).
  */
-#ifndef FORTRAN_ISO_FORTRAN_BINDING_WRAPPER_H_
+#ifndef FORTRAN_COMMON_ISO_FORTRAN_BINDING_WRAPPER_H_
 #include <stddef.h>
 #define FORTRAN_ISO_NAMESPACE_
 #endif
@@ -207,4 +215,4 @@ RT_API_ATTRS int CFI_setpointer(
 } // extern "C"
 #endif
 
-#endif /* CFI_ISO_FORTRAN_BINDING_H_ */
+#endif /* FORTRAN_ISO_FORTRAN_BINDING_H_ */
diff --git a/flang/include/flang/Runtime/README.md b/flang/include/flang/Runtime/README.md
@@ -1,8 +1,8 @@
-Files in this directory are used by Flang (the compiler) and FortranRuntime
+Files in this directory are used by Flang (the compiler) and flang-rt
 (the runtime library for Flang-compiled programs). They must be compatible by
 both. For definitions used only by Flang, consider
 `flang/{lib,include/flang}/Support` instead. For definitions used only by
-FortranRuntime, consider `FortranRuntime/{lib,include/FortranRuntime}/Runtime`.
+the runtime, consider `flang-rt/{lib,include/flang-rt}/flang_rt`.
 
 The requirements for common code include:
 

diff --git a/flang/include/flang/Testing/README.md b/flang/include/flang/Testing/README.md
@@ -1,8 +1,8 @@
-Files in this directory are used by Flang (the compiler) and FortranRuntime
+Files in this directory are used by Flang (the compiler) and flang-rt
 (the runtime library for Flang-compiled programs). They must be compatible by
 both. For definitions used only by Flang, consider
 `flang/{lib,include/flang}/Support` instead. For definitions used only by
-FortranRuntime, consider `FortranRuntime/{lib,include/FortranRuntime}/Runtime`.
+the runtime, consider `flang-rt/{lib,include/flang-rt}/flang_rt`.
 
 The requirements for common code include:
 
@@ -23,3 +23,5 @@ The requirements for common code include:
 
  * Global declarations may need to be annotated using definitions from
    `api-attrs.h`.
+
+ * The `Runtime` component is header-only.
diff --git a/flang/lib/Common/README.md b/flang/lib/Common/README.md
@@ -1,8 +1,8 @@
-Files in this directory are used by Flang (the compiler) and FortranRuntime
+Files in this directory are used by Flang (the compiler) and flang-rt
 (the runtime library for Flang-compiled programs). They must be compatible by
 both. For definitions used only by Flang, consider
 `flang/{lib,include/flang}/Support` instead. For definitions used only by
-FortranRuntime, consider `FortranRuntime/{lib,include/FortranRuntime}/Runtime`.
+the runtime, consider `flang-rt/{lib,include/flang-rt}/flang_rt`.
 
 The requirements for common code include:
 
@@ -23,3 +23,5 @@ The requirements for common code include:
 
  * Global declarations may need to be annotated using definitions from
    `api-attrs.h`.
+
+ * The `Runtime` component is header-only.
diff --git a/flang/lib/Optimizer/Builder/IntrinsicCall.cpp b/flang/lib/Optimizer/Builder/IntrinsicCall.cpp
@@ -751,7 +751,7 @@ prettyPrintIntrinsicName(fir::FirOpBuilder &builder, mlir::Location loc,
 // Generate a call to the Fortran runtime library providing
 // support for 128-bit float math.
 // On 'LDBL_MANT_DIG == 113' targets the implementation
-// is provided by FortranRuntime, otherwise, it is done via
+// is provided by flang-rt, otherwise, it is done via
 // FortranFloat128Math library. In the latter case the compiler
 // has to be built with FLANG_RUNTIME_F128_MATH_LIB to guarantee
 // proper linking actions in the driver.

diff --git a/flang/lib/Optimizer/Transforms/CufOpConversion.cpp b/flang/lib/Optimizer/Transforms/CufOpConversion.cpp
@@ -1,4 +1,4 @@
-//===-- CufOpConversion.cpp -----------------------------------------------===//
+//===-- lib/Optimizer/Transforms/CufOpConversion.cpp ------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.

diff --git a/flang/lib/Testing/CMakeLists.txt b/flang/lib/Testing/CMakeLists.txt
diff --git a/flang/lib/Testing/README.md b/flang/lib/Testing/README.md
@@ -1,8 +1,8 @@
-Files in this directory are used by Flang (the compiler) and FortranRuntime
+Files in this directory are used by Flang (the compiler) and flang-rt
 (the runtime library for Flang-compiled programs). They must be compatible by
 both. For definitions used only by Flang, consider
 `flang/{lib,include/flang}/Support` instead. For definitions used only by
-FortranRuntime, consider `FortranRuntime/{lib,include/FortranRuntime}/Runtime`.
+the runtime, consider `flang-rt/{lib,include/flang-rt}/flang_rt`.
 
 The requirements for common code include:
 
@@ -23,3 +23,5 @@ The requirements for common code include:
 
  * Global declarations may need to be annotated using definitions from
    `api-attrs.h`.
+
+ * The `Runtime` component is header-only.
diff --git a/...time/lib/Runtime/iso_fortran_env_impl.f90 → flang/module/iso_fortran_env_impl.f90 b/...time/lib/Runtime/iso_fortran_env_impl.f90 → flang/module/iso_fortran_env_impl.f90
@@ -1,4 +1,4 @@
-!===-- lib/Runtime/iso_fortran_env_impl.f90 --------------------------------===!
+!===-- module/iso_fortran_env_impl.f90 --=--------------------------------===!
 !
 ! Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 ! See https://llvm.org/LICENSE.txt for license information.
@@ -8,7 +8,7 @@
 
 ! This MODULE implements part of the ISO_FORTRAN_ENV module file, which
 ! partially requires linkable symbols for some entities defined
-! (e.g., real_kinds).
+! (e.g., real_kinds). Hence, this file is also used by Flang-RT.
 
 module iso_fortran_env_impl
   implicit none

diff --git a/flang/test/Driver/gcc-toolchain-install-dir.f90 b/flang/test/Driver/gcc-toolchain-install-dir.f90
@@ -1,5 +1,5 @@
 !! Test that --gcc-toolchain and --gcc-install-dir options are working as expected.
-!! It does not test cross-compiling (--sysroot), so crtbegin.o, libgcc/compiler-rt, libc, libFortranRuntime, etc. are not supposed to be affected.
+!! It does not test cross-compiling (--sysroot), so crtbegin.o, libgcc/compiler-rt, libc, libflang_rt, etc. are not supposed to be affected.
 !! PREFIX is captured twice because the driver escapes backslashes (occuring in Windows paths) in the -### output, but not on the "Selected GCC installation:" line.
 
 ! RUN: %flang 2>&1 -### -v -o %t %s -no-integrated-as -fuse-ld=ld --target=i386-unknown-linux-gnu --gcc-install-dir=%S/Inputs/basic_cross_linux_tree/usr/lib/gcc/i386-unknown-linux-gnu/10.2.0 | FileCheck %s --check-prefix=CHECK-I386

diff --git a/flang/test/Driver/linker-flags.f90 b/flang/test/Driver/linker-flags.f90
@@ -33,26 +33,26 @@
 ! SOLARIS-F128NONE-NOT: FortranFloat128Math
 ! UNIX-F128LIBQUADMATH-SAME: "-lFortranFloat128Math" "--as-needed" "-lquadmath" "--no-as-needed"
 ! SOLARIS-F128LIBQUADMATH-SAME: "-lFortranFloat128Math" "-z" "ignore" "-lquadmath" "-z" "record"
-! UNIX-SAME: "-lFortranRuntime" "-lm"
+! UNIX-SAME: "-lflang_rt" "-lm"
 ! COMPILER-RT: "{{.*}}{{\\|/}}libclang_rt.builtins.a"
 
 ! DARWIN-LABEL:  "{{.*}}ld{{(\.exe)?}}"
 ! DARWIN-SAME: "[[object_file]]"
 ! DARWIN-F128NONE-NOT: FortranFloat128Math
 ! DARWIN-F128LIBQUADMATH-SAME: "-lFortranFloat128Math" "--as-needed" "-lquadmath" "--no-as-needed"
-! DARWIN-SAME: -lFortranRuntime
+! DARWIN-SAME: -lflang_rt
 
 ! HAIKU-LABEL:  "{{.*}}ld{{(\.exe)?}}"
 ! HAIKU-SAME: "[[object_file]]"
 ! HAIKU-F128NONE-NOT: FortranFloat128Math
 ! HAIKU-F128LIBQUADMATH-SAME: "-lFortranFloat128Math" "--as-needed" "-lquadmath" "--no-as-needed"
-! HAIKU-SAME: "-lFortranRuntime"
+! HAIKU-SAME: "-lflang_rt"
 
 ! MINGW-LABEL:  "{{.*}}ld{{(\.exe)?}}"
 ! MINGW-SAME: "[[object_file]]"
 ! MINGW-F128NONE-NOT: FortranFloat128Math
 ! MINGW-F128LIBQUADMATH-SAME: "-lFortranFloat128Math" "--as-needed" "-lquadmath" "--no-as-needed"
-! MINGW-SAME: -lFortranRuntime
+! MINGW-SAME: -lflang_rt
 
 ! NOTE: This also matches lld-link (when CLANG_DEFAULT_LINKER=lld) and
 !       any .exe suffix that is added when resolving to the full path of

diff --git a/flang/test/Driver/msvc-dependent-lib-flags.f90 b/flang/test/Driver/msvc-dependent-lib-flags.f90
@@ -6,23 +6,23 @@
 ! MSVC: -fc1
 ! MSVC-SAME: -D_MT
 ! MSVC-SAME: --dependent-lib=libcmt
-! MSVC-SAME: --dependent-lib=FortranRuntime.static.lib
+! MSVC-SAME: --dependent-lib=flang_rt.static.lib
 
 ! MSVC-DEBUG: -fc1
 ! MSVC-DEBUG-SAME: -D_MT
 ! MSVC-DEBUG-SAME: -D_DEBUG
 ! MSVC-DEBUG-SAME: --dependent-lib=libcmtd
-! MSVC-DEBUG-SAME: --dependent-lib=FortranRuntime.static_dbg.lib
+! MSVC-DEBUG-SAME: --dependent-lib=flang_rt.static_dbg.lib
 
 ! MSVC-DLL: -fc1
 ! MSVC-DLL-SAME: -D_MT
 ! MSVC-DLL-SAME: -D_DLL
 ! MSVC-DLL-SAME: --dependent-lib=msvcrt
-! MSVC-DLL-SAME: --dependent-lib=FortranRuntime.dynamic.lib
+! MSVC-DLL-SAME: --dependent-lib=flang_rt.dynamic.lib
 
 ! MSVC-DLL-DEBUG: -fc1
 ! MSVC-DLL-DEBUG-SAME: -D_MT
 ! MSVC-DLL-DEBUG-SAME: -D_DEBUG
 ! MSVC-DLL-DEBUG-SAME: -D_DLL
 ! MSVC-DLL-DEBUG-SAME: --dependent-lib=msvcrtd
-! MSVC-DLL-DEBUG-SAME: --dependent-lib=FortranRuntime.dynamic_dbg.lib
+! MSVC-DLL-DEBUG-SAME: --dependent-lib=flang_rt.dynamic_dbg.lib
diff --git a/flang/tools/f18/CMakeLists.txt b/flang/tools/f18/CMakeLists.txt
@@ -54,8 +54,6 @@ if (NOT CMAKE_CROSSCOMPILING)
   foreach(filename ${MODULES})
     set(depends "")
     set(opts "")
-    set(sourcepath "${FLANG_SOURCE_DIR}/module/${filename}.f90")
-    set(modpath "${FLANG_INTRINSIC_MODULES_DIR}/${filename}.mod")
     if(${filename} STREQUAL "__fortran_builtins" OR
        ${filename} STREQUAL "__ppc_types")
     elseif(${filename} STREQUAL "__ppc_intrinsics" OR
@@ -66,9 +64,6 @@ if (NOT CMAKE_CROSSCOMPILING)
       set(depends ${FLANG_INTRINSIC_MODULES_DIR}/__cuda_builtins.mod)
     else()
       set(depends ${FLANG_INTRINSIC_MODULES_DIR}/__fortran_builtins.mod)
-      if(${filename} STREQUAL "iso_fortran_env_impl")
-        set(sourcepath "${FORTRANRUNTIME_SOURCE_DIR}/lib/Runtime/${filename}.f90")
-      endif()
       if(${filename} STREQUAL "iso_fortran_env")
         set(depends ${depends} ${FLANG_INTRINSIC_MODULES_DIR}/iso_fortran_env_impl.mod)
       endif()
@@ -97,27 +92,20 @@ if (NOT CMAKE_CROSSCOMPILING)
       set(decls "-DFLANG_SUPPORT_R16")
     endif()
 
-    # Some modules have an implementation part that needs to be added to the
-    # FortranRuntime library.
     set(compile_with "-fsyntax-only")
     set(object_output "")
     set(include_in_link FALSE)
 
+    set(base ${FLANG_INTRINSIC_MODULES_DIR}/${filename})
     # TODO: We may need to flag this with conditional, in case Flang is built w/o OpenMP support
-    add_custom_command(OUTPUT ${modpath} ${object_output}
+    add_custom_command(OUTPUT ${base}.mod ${object_output}
       COMMAND ${CMAKE_COMMAND} -E make_directory ${FLANG_INTRINSIC_MODULES_DIR}
       COMMAND flang-new ${opts} ${decls} -cpp ${compile_with} -module-dir ${FLANG_INTRINSIC_MODULES_DIR}
-        ${sourcepath}
-      DEPENDS flang-new ${sourcepath} ${FLANG_SOURCE_DIR}/module/__fortran_builtins.f90 ${depends}
+        ${FLANG_SOURCE_DIR}/module/${filename}.f90
+      DEPENDS flang-new ${FLANG_SOURCE_DIR}/module/${filename}.f90 ${FLANG_SOURCE_DIR}/module/__fortran_builtins.f90 ${depends}
     )
-    list(APPEND MODULE_FILES "${modpath}")
-    install(FILES "${modpath}" DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/flang")
-
-    # If a module has been compiled into an object file, add the file to
-    # the link line for the FortranRuntime library.
-    if(include_in_link)
-      list(APPEND module_objects ${object_output})
-    endif()
+    list(APPEND MODULE_FILES ${base}.mod)
+    install(FILES ${base}.mod DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/flang")
   endforeach()
 
   # Special case for omp_lib.mod, because its source comes from openmp/runtime/src/include.

diff --git a/flang/unittests/Common/CMakeLists.txt b/flang/unittests/Common/CMakeLists.txt
@@ -6,8 +6,8 @@
 #
 #===------------------------------------------------------------------------===#
 
-add_fortranruntime_unittest(FlangCommonTests
+add_flangrt_unittest(FlangCommonTests
   FastIntSetTest.cpp
   LINK_LIBS
-    FortranRuntime.unittest
+    flang_rt.unittest
 )
diff --git a/flang/unittests/Decimal/CMakeLists.txt b/flang/unittests/Decimal/CMakeLists.txt
@@ -6,15 +6,15 @@
 #
 #===------------------------------------------------------------------------===#
 
-add_fortranruntime_nongtest_unittest(quick-sanity-test
+add_flangrt_nongtest_unittest(quick-sanity-test
 quick-sanity-test.cpp
 LINK_LIBS
-  FortranRuntime.unittest
+  flang_rt.unittest
 )
 
 # This test is not run by default as it takes a long time to execute.
-add_fortranruntime_nongtest_unittest(thorough-test SLOW_TEST
+add_flangrt_nongtest_unittest(thorough-test SLOW_TEST
 thorough-test.cpp
 LINK_LIBS
-  FortranRuntime.unittest
+  flang_rt.unittest
 )
diff --git a/lld/COFF/MinGW.cpp b/lld/COFF/MinGW.cpp
@@ -50,11 +50,11 @@ AutoExporter::AutoExporter(
       "libclang_rt.profile-x86_64",
       "libc++",
       "libc++abi",
-      "libFortranRuntime",
-      "libFortranRuntime.static",
-      "libFortranRuntime.dynamic",
-      "libFortranRuntime.static_dbg",
-      "libFortranRuntime.dynamic_dbg",
+      "libflang_rt",
+      "libflang_rt.static",
+      "libflang_rt.dynamic",
+      "libflang_rtstatic_dbg",
+      "libflang_rt.dynamic_dbg",
       "libunwind",
       "libmsvcrt",
       "libucrtbase",

diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
@@ -149,7 +149,7 @@ endif()
 # As we migrate runtimes to using the bootstrapping build, the set of default runtimes
 # should grow as we remove those runtimes from LLVM_ENABLE_PROJECTS above.
 set(LLVM_DEFAULT_RUNTIMES "libcxx;libcxxabi;libunwind")
-set(LLVM_SUPPORTED_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;llvm-libgcc;offload;FortranRuntime")
+set(LLVM_SUPPORTED_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;llvm-libgcc;offload;flang-rt")
 set(LLVM_ENABLE_RUNTIMES "" CACHE STRING
   "Semicolon-separated list of runtimes to build, or \"all\" (${LLVM_DEFAULT_RUNTIMES}). Supported runtimes are ${LLVM_SUPPORTED_RUNTIMES}.")
 if(LLVM_ENABLE_RUNTIMES STREQUAL "all")

diff --git a/llvm/projects/CMakeLists.txt b/llvm/projects/CMakeLists.txt
@@ -12,7 +12,7 @@ foreach(entry ${entries})
        (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/test-suite) AND
        (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/openmp) AND
        (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/cross-project-tests) AND
-       (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/FortranRuntime))
+       (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/flang-rt))
       get_filename_component(entry_name "${entry}" NAME)
       add_llvm_external_project(${entry_name})
     endif()
@@ -38,7 +38,7 @@ if(${LLVM_BUILD_RUNTIME})
   if(NOT LLVM_BUILD_EXTERNAL_COMPILER_RT)
     add_llvm_external_project(compiler-rt)
   endif()
-  add_llvm_external_project(FortranRuntime)
+  add_llvm_external_project(flang-rt)
 endif()
 
 add_llvm_external_project(dragonegg)

diff --git a/llvm/runtimes/CMakeLists.txt b/llvm/runtimes/CMakeLists.txt
@@ -280,8 +280,8 @@ function(runtime_default_target)
                                       ${ARG_CMAKE_ARGS}
                            PASSTHROUGH_PREFIXES LLVM_ENABLE_RUNTIMES
                                                 LLVM_USE_LINKER
-                                                CUDA # For runtimes that may look for the CUDA SDK (libc, offload)
-                                                FLANG_RUNTIME # Shared between Flang and FortranRuntime
+                                                CUDA # For runtimes that may look for the CUDA SDK (libc, offload, flang-rt)
+                                                FLANG_RUNTIME # Shared between Flang and Flang-RT
                                                 ${ARG_PREFIXES}
                            EXTRA_TARGETS ${extra_targets}
                                          ${test_targets}
@@ -573,7 +573,7 @@ if(build_runtimes)
   if(LLVM_LIBC_FULL_BUILD)
     list(APPEND extra_cmake_args "-DLLVM_LIBC_FULL_BUILD=ON")
   endif()
-  if("FortranRuntime" IN_LIST LLVM_ENABLE_RUNTIMES)
+  if("flang-rt" IN_LIST LLVM_ENABLE_RUNTIMES)
     set(enable_fortran ENABLE_FORTRAN)
   endif ()
 

diff --git a/runtimes/CMakeLists.txt b/runtimes/CMakeLists.txt
@@ -23,8 +23,8 @@ list(INSERT CMAKE_MODULE_PATH 0
 
 # We order libraries to mirror roughly how they are layered, except that compiler-rt can depend
 # on libc++, so we put it after.
-set(LLVM_DEFAULT_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;offload;FortranRuntime")
-set(LLVM_SUPPORTED_RUNTIMES "${LLVM_DEFAULT_RUNTIMES};llvm-libgcc")
+set(LLVM_DEFAULT_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;offload")
+set(LLVM_SUPPORTED_RUNTIMES "${LLVM_DEFAULT_RUNTIMES};llvm-libgcc;flang-rt")
 set(LLVM_ENABLE_RUNTIMES "" CACHE STRING
   "Semicolon-separated list of runtimes to build, or \"all\" (${LLVM_DEFAULT_RUNTIMES}). Supported runtimes are ${LLVM_SUPPORTED_RUNTIMES}.")
 if(LLVM_ENABLE_RUNTIMES STREQUAL "all" )