diff --git a/libcxx/docs/Status/RangesAlgorithms.csv b/libcxx/docs/Status/RangesAlgorithms.csv
--- a/libcxx/docs/Status/RangesAlgorithms.csv
+++ b/libcxx/docs/Status/RangesAlgorithms.csv
@@ -49,8 +49,8 @@
Write,generate_n,Not assigned,n/a,Not started
Write,remove_copy,Not assigned,n/a,Not started
Write,remove_copy_if,Not assigned,n/a,Not started
-Write,replace,Not assigned,n/a,Not started
-Write,replace_if,Not assigned,n/a,Not started
+Write,replace,Nikolas Klauser,` `_,✅
+Write,replace_if,Nikolas Klauser,` `_,✅
Write,replace_copy,Not assigned,n/a,Not started
Write,replace_copy_if,Not assigned,n/a,Not started
Write,swap_ranges,Nikolas Klauser,`D116303 `_,✅
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -85,6 +85,8 @@
__algorithm/ranges_minmax.h
__algorithm/ranges_minmax_element.h
__algorithm/ranges_mismatch.h
+ __algorithm/ranges_replace.h
+ __algorithm/ranges_replace_if.h
__algorithm/ranges_swap_ranges.h
__algorithm/ranges_transform.h
__algorithm/remove.h
diff --git a/libcxx/include/__algorithm/ranges_replace.h b/libcxx/include/__algorithm/ranges_replace.h
new file mode 100644
--- /dev/null
+++ b/libcxx/include/__algorithm/ranges_replace.h
@@ -0,0 +1,70 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 _LIBCPP___ALGORITHM_RANGES_REPLACE_H
+#define _LIBCPP___ALGORITHM_RANGES_REPLACE_H
+
+#include <__algorithm/ranges_replace_if.h>
+#include <__config>
+#include <__functional/identity.h>
+#include <__functional/ranges_operations.h>
+#include <__iterator/concepts.h>
+#include <__iterator/projected.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__ranges/dangling.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+# pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+namespace __replace {
+struct __fn {
+
+ template _Sent,
+ class _Type1,
+ class _Type2,
+ class _Proj = identity>
+ requires indirectly_writable<_Iter, const _Type2&>
+ && indirect_binary_predicate, const _Type1*>
+ _LIBCPP_HIDE_FROM_ABI constexpr
+ _Iter operator()(_Iter __first, _Sent __last,
+ const _Type1& __old_value,
+ const _Type2& __new_value,
+ _Proj __proj = {}) const {
+ auto __pred = [&](auto&& __val) { return __val == __old_value; };
+ return ranges::__replace_if_impl(std::move(__first), std::move(__last), __pred, __new_value, __proj);
+ }
+
+ template
+ requires indirectly_writable, const _Type2&>
+ && indirect_binary_predicate, _Proj>, const _Type1*>
+ _LIBCPP_HIDE_FROM_ABI constexpr borrowed_iterator_t<_Range>
+ operator()(_Range&& __range, const _Type1& __old_value, const _Type2& __new_value, _Proj __proj = {}) const {
+ auto __pred = [&](auto&& __val) { return __val == __old_value; };
+ return ranges::__replace_if_impl(ranges::begin(__range), ranges::end(__range), __pred, __new_value, __proj);
+ }
+
+};
+} // namespace __replace
+
+inline namespace __cpo {
+ inline constexpr auto replace = __replace::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___ALGORITHM_RANGES_REPLACE_H
diff --git a/libcxx/include/__algorithm/ranges_replace_if.h b/libcxx/include/__algorithm/ranges_replace_if.h
new file mode 100644
--- /dev/null
+++ b/libcxx/include/__algorithm/ranges_replace_if.h
@@ -0,0 +1,73 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 _LIBCPP___ALGORITHM_RANGES_REPLACE_IF_H
+#define _LIBCPP___ALGORITHM_RANGES_REPLACE_IF_H
+
+#include <__config>
+#include <__functional/identity.h>
+#include <__functional/invoke.h>
+#include <__iterator/concepts.h>
+#include <__iterator/projected.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__ranges/dangling.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+# pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+
+template
+_LIBCPP_HIDE_FROM_ABI constexpr
+_Iter __replace_if_impl(_Iter __first, _Sent __last, _Pred& __pred, const _Type& __new_value, _Proj& __proj) {
+ for (; __first != __last; ++__first) {
+ if (std::invoke(__pred, std::invoke(__proj, *__first)))
+ *__first = __new_value;
+ }
+ return __first;
+}
+
+namespace __replace_if {
+struct __fn {
+
+ template _Sent,
+ class _Type,
+ class _Proj = identity,
+ indirect_unary_predicate> _Pred>
+ requires indirectly_writable<_Iter, const _Type&>
+ _LIBCPP_HIDE_FROM_ABI constexpr
+ _Iter operator()(_Iter __first, _Sent __last, _Pred __pred, const _Type& __new_value, _Proj __proj = {}) const {
+ return ranges::__replace_if_impl(std::move(__first), std::move(__last), __pred, __new_value, __proj);
+ }
+
+ template , _Proj>> _Pred>
+ requires indirectly_writable, const _Type&>
+ _LIBCPP_HIDE_FROM_ABI constexpr borrowed_iterator_t<_Range>
+ operator()(_Range&& __range, _Pred __pred, const _Type& __new_value, _Proj __proj = {}) const {
+ return ranges::__replace_if_impl(ranges::begin(__range), ranges::end(__range), __pred, __new_value, __proj);
+ }
+
+};
+} // namespace __replace_if
+
+inline namespace __cpo {
+ inline constexpr auto replace_if = __replace_if::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___ALGORITHM_RANGES_REPLACE_IF_H
diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -1000,6 +1000,8 @@
#include <__algorithm/ranges_minmax.h>
#include <__algorithm/ranges_minmax_element.h>
#include <__algorithm/ranges_mismatch.h>
+#include <__algorithm/ranges_replace.h>
+#include <__algorithm/ranges_replace_if.h>
#include <__algorithm/ranges_swap_ranges.h>
#include <__algorithm/ranges_transform.h>
#include <__algorithm/remove.h>
diff --git a/libcxx/include/module.modulemap b/libcxx/include/module.modulemap
--- a/libcxx/include/module.modulemap
+++ b/libcxx/include/module.modulemap
@@ -318,6 +318,8 @@
module ranges_minmax { private header "__algorithm/ranges_minmax.h" }
module ranges_minmax_element { private header "__algorithm/ranges_minmax_element.h" }
module ranges_mismatch { private header "__algorithm/ranges_mismatch.h" }
+ module ranges_replace { private header "__algorithm/ranges_replace.h" }
+ module ranges_replace_if { private header "__algorithm/ranges_replace_if.h" }
module ranges_swap_ranges { private header "__algorithm/ranges_swap_ranges.h" }
module ranges_transform { private header "__algorithm/ranges_transform.h" }
module remove { private header "__algorithm/remove.h" }
diff --git a/libcxx/test/libcxx/private_headers.verify.cpp b/libcxx/test/libcxx/private_headers.verify.cpp
--- a/libcxx/test/libcxx/private_headers.verify.cpp
+++ b/libcxx/test/libcxx/private_headers.verify.cpp
@@ -122,6 +122,8 @@
#include <__algorithm/ranges_minmax.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_minmax.h'}}
#include <__algorithm/ranges_minmax_element.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_minmax_element.h'}}
#include <__algorithm/ranges_mismatch.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_mismatch.h'}}
+#include <__algorithm/ranges_replace.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_replace.h'}}
+#include <__algorithm/ranges_replace_if.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_replace_if.h'}}
#include <__algorithm/ranges_swap_ranges.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_swap_ranges.h'}}
#include <__algorithm/ranges_transform.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_transform.h'}}
#include <__algorithm/remove.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/remove.h'}}
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.replace/ranges.replace.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.replace/ranges.replace.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.replace/ranges.replace.pass.cpp
@@ -0,0 +1,86 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-has-no-incomplete-ranges
+
+#include
+#include
+#include
+#include
+
+#include "test_iterators.h"
+
+template
+constexpr void test(std::array a_, int oldval, int newval, std::array expected) {
+ {
+ auto a = a_;
+ std::same_as auto ret = std::ranges::replace(Iter(a.data()), Sent(Iter(a.data() + N)),
+ oldval,
+ newval);
+ assert(base(ret) == a.data() + N);
+ assert(a == expected);
+ }
+ {
+ auto a = a_;
+ auto range = std::ranges::subrange(Iter(a.data()), Sent(Iter(a.data() + N)));
+ std::same_as auto ret = std::ranges::replace(range, oldval, newval);
+ assert(base(ret) == a.data() + N);
+ assert(a == expected);
+ }
+}
+
+template
+constexpr void test_iterators() {
+ // simple test
+ test({1, 2, 3, 4}, 2, 23, {1, 23, 3, 4});
+ // no match
+ test({1, 2, 3, 4}, 5, 23, {1, 2, 3, 4});
+ // all match
+ test({1, 1, 1, 1}, 1, 23, {23, 23, 23, 23});
+ // empty range
+ test({}, 1, 23, {});
+ // single element range
+ test({1}, 1, 2, {2});
+}
+
+constexpr bool test() {
+ test_iterators, sentinel_wrapper>>();
+ test_iterators, sentinel_wrapper>>();
+ test_iterators>();
+ test_iterators>();
+ test_iterators>();
+ test_iterators>();
+ test_iterators();
+
+ { // check that the projection is used
+ struct S {
+ constexpr S(int i_) : i(i_) {}
+ int i;
+ };
+ {
+ S a[] = {1, 2, 3, 4};
+ std::ranges::replace(a, a + 4, 3, S{0}, &S::i);
+ }
+ {
+ S a[] = {1, 2, 3, 4};
+ std::ranges::replace(a, 3, S{0}, &S::i);
+ }
+ }
+
+ return true;
+}
+
+int main(int, char**) {
+ test();
+ static_assert(test());
+
+ return 0;
+}
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.replace/ranges.replace_if.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.replace/ranges.replace_if.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.replace/ranges.replace_if.pass.cpp
@@ -0,0 +1,86 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-has-no-incomplete-ranges
+
+#include
+#include
+#include
+#include
+
+#include "test_iterators.h"
+
+template
+constexpr void test(std::array a_, Pred pred, int val, std::array expected) {
+ {
+ auto a = a_;
+ std::same_as auto ret = std::ranges::replace_if(Iter(a.data()), Sent(Iter(a.data() + N)),
+ pred,
+ val);
+ assert(base(ret) == a.data() + N);
+ assert(a == expected);
+ }
+ {
+ auto a = a_;
+ auto range = std::ranges::subrange(Iter(a.data()), Sent(Iter(a.data() + N)));
+ std::same_as auto ret = std::ranges::replace_if(range, pred, val);
+ assert(base(ret) == a.data() + N);
+ assert(a == expected);
+ }
+}
+
+template
+constexpr void test_iterators() {
+ // simple test
+ test({1, 2, 3, 4}, [](int i) { return i < 3; }, 23, {23, 23, 3, 4});
+ // no match
+ test({1, 2, 3, 4}, [](int i) { return i < 0; }, 23, {1, 2, 3, 4});
+ // all match
+ test({1, 2, 3, 4}, [](int i) { return i > 0; }, 23, {23, 23, 23, 23});
+ // empty range
+ test({}, [](int i) { return i > 0; }, 23, {});
+ // single element range
+ test({1}, [](int i) { return i > 0; }, 2, {2});
+}
+
+constexpr bool test() {
+ test_iterators, sentinel_wrapper>>();
+ test_iterators, sentinel_wrapper>>();
+ test_iterators>();
+ test_iterators>();
+ test_iterators>();
+ test_iterators>();
+ test_iterators();
+
+ { // check that the projection is used
+ struct S {
+ constexpr S(int i_) : i(i_) {}
+ int i;
+ };
+ {
+ S a[] = {1, 2, 3, 4};
+ std::ranges::replace_if(a, a + 4, [](int i) { return i == 3; }, S{0}, &S::i);
+ }
+ {
+ S a[] = {1, 2, 3, 4};
+ std::ranges::replace_if(a, [](int i) { return i == 3; }, S{0}, &S::i);
+ }
+ }
+
+ return true;
+}
+
+int main(int, char**) {
+ test();
+ static_assert(test());
+
+ return 0;
+}