diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -490,6 +490,20 @@
   set(LIBCXX_DEBUG_BUILD OFF)
 endif()
 
+# PSTL Configuration ===========================================================
+if (LIBCXX_ENABLE_PARALLEL_ALGORITHMS)
+  get_target_property(LIBCXXABI_PSTL_INCLUDE_DIRS pstl::ParallelSTL INTERFACE_INCLUDE_DIRECTORIES)
+  list(POP_FRONT LIBCXXABI_PSTL_INCLUDE_DIRS LIBCXX_PSTL_SOURCE_DIR LIBCXX_PSTL_GENERATED_SOURCE_DIR)
+
+  string(LENGTH ${LIBCXX_PSTL_SOURCE_DIR} length)
+  math(EXPR length "${length} - 19")
+  string(SUBSTRING ${LIBCXX_PSTL_SOURCE_DIR} 18 ${length} LIBCXX_PSTL_SOURCE_DIR)
+
+  string(LENGTH ${LIBCXX_PSTL_GENERATED_SOURCE_DIR} length)
+  math(EXPR length "${length} - 19")
+  string(SUBSTRING ${LIBCXX_PSTL_GENERATED_SOURCE_DIR} 18 ${length} LIBCXX_PSTL_GENERATED_SOURCE_DIR)
+endif()
+
 #===============================================================================
 # Setup Compiler Flags
 #===============================================================================
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -801,6 +801,48 @@
   wctype.h
   )
 
+set(pstl_files
+    __pstl_algorithm
+    __pstl_execution
+    __pstl_memory
+    __pstl_numeric
+    pstl/internal/omp/parallel_for_each.h
+    pstl/internal/omp/parallel_for.h
+    pstl/internal/omp/parallel_invoke.h
+    pstl/internal/omp/parallel_merge.h
+    pstl/internal/omp/parallel_reduce.h
+    pstl/internal/omp/parallel_scan.h
+    pstl/internal/omp/parallel_stable_partial_sort.h
+    pstl/internal/omp/parallel_stable_sort.h
+    pstl/internal/omp/parallel_transform_reduce.h
+    pstl/internal/omp/parallel_transform_scan.h
+    pstl/internal/omp/util.h
+    pstl/internal/algorithm_fwd.h
+    pstl/internal/algorithm_impl.h
+    pstl/internal/execution_defs.h
+    pstl/internal/execution_impl.h
+    pstl/internal/glue_algorithm_defs.h
+    pstl/internal/glue_algorithm_impl.h
+    pstl/internal/glue_execution_defs.h
+    pstl/internal/glue_memory_defs.h
+    pstl/internal/glue_memory_impl.h
+    pstl/internal/glue_numeric_defs.h
+    pstl/internal/glue_numeric_impl.h
+    pstl/internal/memory_impl.h
+    pstl/internal/numeric_fwd.h
+    pstl/internal/numeric_impl.h
+    pstl/internal/parallel_backend_omp.h
+    pstl/internal/parallel_backend_serial.h
+    pstl/internal/parallel_backend_tbb.h
+    pstl/internal/parallel_backend_utils.h
+    pstl/internal/parallel_backend.h
+    pstl/internal/parallel_impl.h
+    pstl/internal/pstl_config.h
+    pstl/internal/undef_macros.h
+    pstl/internal/unseq_backend_simd.h
+    pstl/internal/utils.h
+   )
+
 foreach(feature LIBCXX_ENABLE_FILESYSTEM LIBCXX_ENABLE_LOCALIZATION LIBCXX_ENABLE_THREADS LIBCXX_ENABLE_WIDE_CHARACTERS)
   if (NOT ${${feature}})
     set(requires_${feature} "requires LIBCXX_CONFIGURED_WITHOUT_SUPPORT_FOR_THIS_HEADER")
@@ -822,6 +864,27 @@
   list(APPEND _all_includes "${dst}")
 endforeach()
 
+if (LIBCXX_ENABLE_PARALLEL_ALGORITHMS)
+  message(STATUS "Copying PSTL files")
+  foreach(f ${pstl_files})
+    set(src ${LIBCXX_PSTL_SOURCE_DIR}/${f})
+    set(dst ${LIBCXX_GENERATED_INCLUDE_DIR}/${f})
+    add_custom_command(OUTPUT ${dst}
+                       DEPENDS ${src}
+                       COMMAND ${CMAKE_COMMAND} -E copy_if_different ${src} ${dst}
+                       COMMENT "Copying PSTL header ${f}")
+    list(APPEND _all_includes ${dst})
+  endforeach()
+
+  set(src ${LIBCXX_PSTL_GENERATED_SOURCE_DIR}/__pstl_config_site)
+  set(dst ${LIBCXX_GENERATED_INCLUDE_DIR}/__pstl_config_site)
+  add_custom_command(OUTPUT ${dst}
+                      DEPENDS ${src}
+                      COMMAND ${CMAKE_COMMAND} -E copy_if_different ${src} ${dst}
+                      COMMENT "Copying PSTL header ${f}")
+  list(APPEND _all_includes ${dst})
+endif()
+
 add_custom_target(generate-cxx-headers ALL DEPENDS ${_all_includes})
 
 add_library(cxx-headers INTERFACE)
diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -1913,7 +1913,9 @@
 #endif
 
 #if defined(_LIBCPP_HAS_PARALLEL_ALGORITHMS) && _LIBCPP_STD_VER >= 17
-#   include <__pstl_algorithm>
+// TODO: Remove this include once we fix transitive includes of <algorithm>
+#  include <__functional/not_fn.h>
+#  include <__pstl_algorithm>
 #endif
 
 #endif // _LIBCPP_ALGORITHM
diff --git a/libcxx/include/unordered_map b/libcxx/include/unordered_map
--- a/libcxx/include/unordered_map
+++ b/libcxx/include/unordered_map
@@ -532,7 +532,6 @@
 #include <version>
 
 #ifndef _LIBCPP_REMOVE_TRANSITIVE_INCLUDES
-#  include <algorithm>
 #  include <bit>
 #  include <iterator>
 #endif
diff --git a/libcxx/test/libcxx/clang_tidy.sh.cpp b/libcxx/test/libcxx/clang_tidy.sh.cpp
--- a/libcxx/test/libcxx/clang_tidy.sh.cpp
+++ b/libcxx/test/libcxx/clang_tidy.sh.cpp
@@ -8,6 +8,8 @@
 
 // REQUIRES: has-clang-tidy
 
+// XFAIL: with-pstl
+
 // TODO: run clang-tidy with modules enabled once they are supported
 // RUN: clang-tidy %s --warnings-as-errors=* -header-filter=.* --config-file=%S/../../.clang-tidy -- -Wweak-vtables -Wno-unknown-warning-option %{compile_flags} -fno-modules
 // -Wno-unknown-warning-option tells clang-tidy to ignore '-W' command-line arguments that it doesn't know.
diff --git a/libcxx/test/libcxx/min_max_macros.compile.pass.cpp b/libcxx/test/libcxx/min_max_macros.compile.pass.cpp
--- a/libcxx/test/libcxx/min_max_macros.compile.pass.cpp
+++ b/libcxx/test/libcxx/min_max_macros.compile.pass.cpp
@@ -12,6 +12,8 @@
 // The system-provided <uchar.h> seems to be broken on AIX
 // XFAIL: LIBCXX-AIX-FIXME
 
+// XFAIL: with-pstl
+
 // Prevent <ext/hash_map> from generating deprecated warnings for this test.
 #if defined(__DEPRECATED)
 #    undef __DEPRECATED
diff --git a/libcxx/test/libcxx/nasty_macros.compile.pass.cpp b/libcxx/test/libcxx/nasty_macros.compile.pass.cpp
--- a/libcxx/test/libcxx/nasty_macros.compile.pass.cpp
+++ b/libcxx/test/libcxx/nasty_macros.compile.pass.cpp
@@ -12,6 +12,8 @@
 // The system-provided <uchar.h> seems to be broken on AIX
 // XFAIL: LIBCXX-AIX-FIXME
 
+// XFAIL: with-pstl
+
 // Prevent <ext/hash_map> from generating deprecated warnings for this test.
 #if defined(__DEPRECATED)
 #    undef __DEPRECATED
diff --git a/libcxx/test/libcxx/transitive_includes/expected.unordered_map b/libcxx/test/libcxx/transitive_includes/expected.unordered_map
--- a/libcxx/test/libcxx/transitive_includes/expected.unordered_map
+++ b/libcxx/test/libcxx/transitive_includes/expected.unordered_map
@@ -1,4 +1,3 @@
-algorithm
 atomic
 bit
 chrono
diff --git a/libcxx/utils/ci/buildkite-pipeline.yml b/libcxx/utils/ci/buildkite-pipeline.yml
--- a/libcxx/utils/ci/buildkite-pipeline.yml
+++ b/libcxx/utils/ci/buildkite-pipeline.yml
@@ -392,6 +392,19 @@
           limit: 2
     timeout_in_minutes: 120
 
+  - label: "With PSTL support"
+    command: "libcxx/utils/ci/run-buildbot with-pstl"
+    artifact_paths:
+      - "**/test-results.xml"
+    agents:
+      queue: "libcxx-builders"
+      os: "linux"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
+    timeout_in_minutes: 120
+
   - label: "No transitive includes"
     command: "libcxx/utils/ci/run-buildbot generic-no-transitive-includes"
     artifact_paths:
diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -92,7 +92,7 @@
 
 function generate-cmake() {
     generate-cmake-base \
-          -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" \
+          -DLLVM_ENABLE_RUNTIMES="pstl;libcxx;libcxxabi;libunwind" \
           -DLIBCXX_CXX_ABI=libcxxabi \
           "${@}"
 }
@@ -369,6 +369,15 @@
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-abi-unstable.cmake"
     check-runtimes
 ;;
+with-pstl)
+    clean
+    generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-cxx20.cmake" \
+                   -DLIBCXX_TEST_CONFIG="llvm-libc++-with-pstl.cfg.in" \
+                   -DLIBUNWIND_TEST_CONFIG="llvm-libunwind-shared.cfg.in" \
+                   -DCMAKE_BUILD_WITH_INSTALL_RPATH=TRUE \
+                   -DLIBCXX_ENABLE_PARALLEL_ALGORITHMS=ON
+    check-runtimes
+;;
 apple-system)
     clean
 
diff --git a/libcxx/utils/libcxx/test/features.py b/libcxx/utils/libcxx/test/features.py
--- a/libcxx/utils/libcxx/test/features.py
+++ b/libcxx/utils/libcxx/test/features.py
@@ -197,6 +197,7 @@
   '_LIBCPP_HAS_NO_WIDE_CHARACTERS': 'no-wide-characters',
   '_LIBCPP_HAS_NO_UNICODE': 'libcpp-has-no-unicode',
   '_LIBCPP_ENABLE_DEBUG_MODE': 'libcpp-has-debug-mode',
+  '_LIBCPP_HAS_PARALLEL_ALGORITHMS': 'with-pstl',
 }
 for macro, feature in macros.items():
   DEFAULT_FEATURES.append(
diff --git a/libcxxabi/src/CMakeLists.txt b/libcxxabi/src/CMakeLists.txt
--- a/libcxxabi/src/CMakeLists.txt
+++ b/libcxxabi/src/CMakeLists.txt
@@ -160,6 +160,9 @@
 
 # Build the shared library.
 add_library(cxxabi_shared_objects OBJECT EXCLUDE_FROM_ALL ${LIBCXXABI_SOURCES} ${LIBCXXABI_HEADERS})
+if (TARGET pstl::ParallelSTL)
+  target_link_libraries(cxxabi_shared_objects PUBLIC pstl::ParallelSTL)
+endif()
 if (LIBCXXABI_USE_LLVM_UNWINDER)
   if (LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_SHARED_LIBRARY)
     target_link_libraries(cxxabi_shared_objects PUBLIC unwind_shared_objects) # propagate usage requirements
@@ -235,6 +238,9 @@
 
 # Build the static library.
 add_library(cxxabi_static_objects OBJECT EXCLUDE_FROM_ALL ${LIBCXXABI_SOURCES} ${LIBCXXABI_HEADERS})
+if (TARGET pstl::ParallelSTL)
+  target_link_libraries(cxxabi_static_objects PUBLIC pstl::ParallelSTL)
+endif()
 if (LIBCXXABI_USE_LLVM_UNWINDER AND LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_STATIC_LIBRARY)
   target_link_libraries(cxxabi_static_objects PUBLIC unwind_static_objects) # propagate usage requirements
   target_sources(cxxabi_static_objects PUBLIC $<TARGET_OBJECTS:unwind_static_objects>)
diff --git a/pstl/include/pstl/internal/algorithm_impl.h b/pstl/include/pstl/internal/algorithm_impl.h
--- a/pstl/include/pstl/internal/algorithm_impl.h
+++ b/pstl/include/pstl/internal/algorithm_impl.h
@@ -536,7 +536,7 @@
 
 template <class _Tag, class _ExecutionPolicy, class _ForwardIterator, class _Predicate>
 _ForwardIterator
-__pattern_find_if(_Tag __tag, _ExecutionPolicy&&, _ForwardIterator __first, _ForwardIterator __last,
+__pattern_find_if(_Tag, _ExecutionPolicy&&, _ForwardIterator __first, _ForwardIterator __last,
                   _Predicate __pred) noexcept
 {
     return __internal::__brick_find_if(__first, __last, __pred, typename _Tag::__is_vector{});
diff --git a/pstl/include/pstl/internal/undef_macros.h b/pstl/include/pstl/internal/undef_macros.h
new file mode 100644
--- /dev/null
+++ b/pstl/include/pstl/internal/undef_macros.h
@@ -0,0 +1,15 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifdef min
+#  undef min
+#endif
+
+#ifdef max
+#  undef max
+#endif
diff --git a/pstl/include/pstl/internal/utils.h b/pstl/include/pstl/internal/utils.h
--- a/pstl/include/pstl/internal/utils.h
+++ b/pstl/include/pstl/internal/utils.h
@@ -24,6 +24,7 @@
 auto
 __except_handler(_Fp __f) -> decltype(__f())
 {
+#if defined(__cpp_exceptions) && __cpp_exceptions >= 199711L
     try
     {
         return __f();
@@ -36,6 +37,9 @@
     {
         std::terminate(); // Good bye according to the standard [algorithms.parallel.exceptions]
     }
+#else
+    return __f();
+#endif // defined(__cpp_exceptions) && __cpp_exceptions >= 199711L
 }
 
 template <typename _Fp>
diff --git a/runtimes/CMakeLists.txt b/runtimes/CMakeLists.txt
--- a/runtimes/CMakeLists.txt
+++ b/runtimes/CMakeLists.txt
@@ -15,7 +15,7 @@
 
 # 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")
+set(LLVM_DEFAULT_RUNTIMES "libc;libunwind;pstl;libcxxabi;libcxx;compiler-rt;openmp")
 set(LLVM_ALL_RUNTIMES "${LLVM_DEFAULT_RUNTIMES};llvm-libgcc")
 set(LLVM_ENABLE_RUNTIMES "" CACHE STRING
   "Semicolon-separated list of runtimes to build (${LLVM_ALL_RUNTIMES}), or \"all\".")