diff --git a/HelpSource/Classes/String.schelp b/HelpSource/Classes/String.schelp
index 98be127e9c1..ada09a86f4b 100644
--- a/HelpSource/Classes/String.schelp
+++ b/HelpSource/Classes/String.schelp
@@ -383,6 +383,31 @@ code::
 "[xtz]+nd".matchRegexp("xnd"); // true: any combination of x, t, z
 ::
 
+method::replaceRegexp
+This method is used to replace parts of text.
+
+argument::regex
+A perl regular expression (see link::Classes/String#Regular expressions::) with which to match the caller.
+
+argument::with
+The link::Classes/String:: to replace the found regex with.
+
+returns:: A link::Classes/String::.
+
+code::
+// remove numbers
+"g8et t8ho9se 3num5b89ers ou06t o8f h12er56e!".replaceRegexp("[0-9]", "")
+-> get those numbers out of here!
+
+// remove capital letters
+"HelLO WoRlD".replaceRegexp("(\\\w)", "\\\L$1")
+-> hello world
+
+// remove all capital letter unless at the start of a word
+"HelLO worLD! I weNT tO Paris yeSTErDay.".replaceRegexp("(\\\S)(\\\S*)", "$1\\\L$2")
+-> Hello world! I went to Paris yesterday.
+::
+
 method::findRegexp
 Perl regular expression search (see link::Classes/String#Regular expressions::). This method searches exhaustively for matches and collects them into an array of pairs, in the format code::[character index, matching string]::.
 
diff --git a/SCClassLibrary/Common/Collections/String.sc b/SCClassLibrary/Common/Collections/String.sc
index b9b9ecc7775..ca0e76b3929 100644
--- a/SCClassLibrary/Common/Collections/String.sc
+++ b/SCClassLibrary/Common/Collections/String.sc
@@ -130,6 +130,7 @@ String[char] : RawArray {
 	format { arg ... items; ^this.prFormat( items.collect(_.asString) ) }
 	prFormat { arg items; _String_Format ^this.primitiveFailed }
 	matchRegexp { arg string, start = 0, end; _String_Regexp ^this.primitiveFailed }
+	replaceRegexp { |regex, with| _String_ReplaceRegex ^this.primitiveFailed }
 
 	fformat { arg ... args;
 		var str, resArgs, val, func;
diff --git a/lang/LangPrimSource/PyrStringPrim.cpp b/lang/LangPrimSource/PyrStringPrim.cpp
index 11feb41577a..992cf267cd8 100644
--- a/lang/LangPrimSource/PyrStringPrim.cpp
+++ b/lang/LangPrimSource/PyrStringPrim.cpp
@@ -269,6 +269,62 @@ class regex_lru_cache {
 
 }
 
+
+int prString_ReplaceRegex(struct VMGlobals* g, int numArgsPushed) {
+    // caches the last 64 boost:regex instances.
+    static detail::regex_lru_cache regex_lru_cache(boost::regex_constants::ECMAScript | boost::regex_constants::nosubs);
+
+
+    PyrSlot* slot_this = g->sp - 2; // source string
+    PyrSlot* slot_regex = g->sp - 1; // find
+    PyrSlot* slot_replace = g->sp; // replace with
+
+    // slot one does not need to be checked as this method should only be called from methods in String,
+    //    or children thereof.
+    if (!isKindOfSlot(slot_regex, class_string)) {
+        SetNil(slot_this);
+        return errWrongType;
+    }
+    if (!isKindOfSlot(slot_replace, class_string)) {
+        SetNil(slot_this);
+        return errWrongType;
+    }
+
+    try {
+        const auto& pattern = regex_lru_cache.get_regex(slotRawString(slot_regex)->s, slotRawString(slot_regex)->size);
+
+        const char* source_start = slotRawString(slot_this)->s;
+        const int source_size = slotRawString(slot_this)->size;
+
+        if (source_size < 0) { // size is signed
+            SetNil(slot_this);
+            return errIntegerOverflow;
+        }
+
+        std::string out {};
+        // PyrStrings are not null terminated so a copy is needed.
+        const auto [replaceError, replace] = slotStrStdStrVal(slot_replace);
+        if (replaceError != errNone) {
+            SetNil(slot_this);
+            return replaceError;
+        }
+
+        boost::regex_replace(std::back_inserter(out), source_start, source_start + source_size, pattern, replace);
+
+        if (out.size() > std::numeric_limits<decltype(PyrObjectHdr {}.size)>::max()) {
+            SetNil(slot_this);
+            return errIntegerOverflow;
+        }
+        SetObject(slot_this, newPyrStringN(g->gc, static_cast<int>(out.size()), 0, true));
+        std::copy(out.begin(), out.end(), slotRawString(slot_this)->s);
+        return errNone;
+    } catch (const std::exception& e) {
+        postfl("Warning: Exception in _String_ReplaceRegex -%s\n", e.what());
+        SetNil(slot_this);
+        return errFailed;
+    };
+}
+
 int prString_Regexp(struct VMGlobals* g, int numArgsPushed) {
     /* not reentrant */
     static detail::regex_lru_cache regex_lru_cache(boost::regex_constants::ECMAScript | boost::regex_constants::nosubs);
@@ -1002,4 +1058,5 @@ void initStringPrimitives() {
     definePrimitive(base, index++, "_String_EscapeChar", prString_EscapeChar, 2, 0);
     definePrimitive(base, index++, "_String_ParseYAML", prString_ParseYAML, 1, 0);
     definePrimitive(base, index++, "_String_ParseYAMLFile", prString_ParseYAMLFile, 1, 0);
+    definePrimitive(base, index++, "_String_ReplaceRegex", prString_ReplaceRegex, 3, 0);
 }
diff --git a/lang/LangSource/PyrErrors.h b/lang/LangSource/PyrErrors.h
index 29dfd39b571..c70cfac9112 100644
--- a/lang/LangSource/PyrErrors.h
+++ b/lang/LangSource/PyrErrors.h
@@ -39,6 +39,7 @@ enum { // primitive errors
     errOutOfMemory,
     errCantCallOS,
     errException,
+    errIntegerOverflow,
 
     errPropertyNotFound = 6000,
 
diff --git a/testsuite/classlibrary/TestStringReplaceRegex.sc b/testsuite/classlibrary/TestStringReplaceRegex.sc
new file mode 100644
index 00000000000..4a0720cb4db
--- /dev/null
+++ b/testsuite/classlibrary/TestStringReplaceRegex.sc
@@ -0,0 +1,30 @@
+TestStringReplaceRegex : UnitTest {
+	test_replace_simple {
+		this.assertEquals(
+			"foo, foo, bar, foo".replaceRegexp("foo", "car"),
+			"car, car, bar, car"
+		);
+	}
+	test_replace_empty {
+		this.assertEquals(
+			"".replaceRegexp("foo", "car"),
+			""
+		);
+	}
+	test_replace_more_complex {
+		this.assertEquals(
+			"texttextte9xtte823x234t".replaceRegexp("[0-9]", ""),
+			"texttexttexttext"
+		);
+		this.assertEquals(
+			"hello--Remove--rem0ve".replaceRegexp("(r|R)em(o|0)ve", ""),
+			"hello----"
+		);
+	}
+	test_replace_captures {
+		this.assertEquals(
+			"HelLO WoRlD".replaceRegexp("(\\\w)", "\\\L$1"),
+			"hello world"
+		)
+	}
+}
\ No newline at end of file