diff --git a/openmp/runtime/CMakeLists.txt b/openmp/runtime/CMakeLists.txt
index 93eb14f10a50a..4597a03b0a255 100644
--- a/openmp/runtime/CMakeLists.txt
+++ b/openmp/runtime/CMakeLists.txt
@@ -469,6 +469,7 @@ endif()
 
 add_subdirectory(src)
 add_subdirectory(test)
+add_subdirectory(unittests)
 
 # make these variables available for tools:
 set(LIBOMP_LIBRARY_DIR ${LIBOMP_LIBRARY_DIR} PARENT_SCOPE)
diff --git a/openmp/runtime/src/CMakeLists.txt b/openmp/runtime/src/CMakeLists.txt
index 5dd7f4b33612d..791f250a3b9ec 100644
--- a/openmp/runtime/src/CMakeLists.txt
+++ b/openmp/runtime/src/CMakeLists.txt
@@ -174,17 +174,26 @@ if(NOT WIN32)
 endif()
 
 # Add the OpenMP library
-libomp_get_ldflags(LIBOMP_CONFIGURED_LDFLAGS)
 
+# First, create an OBJECT library with all the runtime sources.
+# This allows the unittests later to access internal symbols which don't export
+# in libomp.
+add_library(obj.omp OBJECT ${LIBOMP_SOURCE_FILES})
+set_property(TARGET obj.omp PROPERTY FOLDER "OpenMP/Libraries")
+set_property(TARGET obj.omp PROPERTY POSITION_INDEPENDENT_CODE ON)
+
+libomp_get_ldflags(LIBOMP_CONFIGURED_LDFLAGS)
 libomp_get_libflags(LIBOMP_CONFIGURED_LIBFLAGS)
-# Build libomp library. Add LLVMSupport dependency if building in-tree with libomptarget profiling enabled.
+
+# Build libomp library. Add LLVMSupport dependency if building in-tree with
+# libomptarget profiling enabled.
 if(OPENMP_STANDALONE_BUILD OR (NOT OPENMP_ENABLE_LIBOMP_PROFILING))
-  add_library(omp ${LIBOMP_LIBRARY_KIND} ${LIBOMP_SOURCE_FILES})
+  add_library(omp ${LIBOMP_LIBRARY_KIND} $<TARGET_OBJECTS:obj.omp>)
   set_property(TARGET omp PROPERTY FOLDER "OpenMP/Libraries")
   # Linking command will include libraries in LIBOMP_CONFIGURED_LIBFLAGS
   target_link_libraries(omp ${LIBOMP_CONFIGURED_LIBFLAGS} ${LIBOMP_DL_LIBS})
 else()
-  add_llvm_library(omp ${LIBOMP_LIBRARY_KIND} ${LIBOMP_SOURCE_FILES} PARTIAL_SOURCES_INTENDED
+  add_llvm_library(omp ${LIBOMP_LIBRARY_KIND} $<TARGET_OBJECTS:obj.omp> PARTIAL_SOURCES_INTENDED
     LINK_LIBS ${LIBOMP_CONFIGURED_LIBFLAGS} ${LIBOMP_DL_LIBS}
     LINK_COMPONENTS Support
     BUILDTREE_ONLY
@@ -296,7 +305,7 @@ set(LIBOMPTARGET_OPENMP_HOST_RTL_FOLDER "${LIBOMP_LIBRARY_DIR}" CACHE STRING
 # objects depend on : .inc files
 add_custom_target(libomp-needed-headers DEPENDS kmp_i18n_id.inc kmp_i18n_default.inc)
 set_target_properties(libomp-needed-headers PROPERTIES FOLDER "OpenMP/Sourcegenning")
-add_dependencies(omp libomp-needed-headers)
+add_dependencies(obj.omp libomp-needed-headers)
 
 # Windows specific build rules
 if(WIN32)
diff --git a/openmp/runtime/test/Unit/lit.cfg.py b/openmp/runtime/test/Unit/lit.cfg.py
new file mode 100644
index 0000000000000..01bd3d961bf00
--- /dev/null
+++ b/openmp/runtime/test/Unit/lit.cfg.py
@@ -0,0 +1,22 @@
+# -*- Python -*-
+
+# Configuration file for the 'lit' test runner.
+
+import os
+import subprocess
+
+import lit.formats
+
+# name: The name of this test suite.
+config.name = "OpenMP-Unit"
+
+# suffixes: A list of file extensions to treat as test files.
+config.suffixes = []
+
+# test_source_root: The root path where tests are located.
+# test_exec_root: The root path where tests should be run.
+config.test_exec_root = config.openmp_unittests_dir
+config.test_source_root = config.test_exec_root
+
+# testFormat: The test format to use to interpret tests.
+config.test_format = lit.formats.GoogleTest(config.llvm_build_mode, "Tests")
diff --git a/openmp/runtime/test/Unit/lit.site.cfg.py.in b/openmp/runtime/test/Unit/lit.site.cfg.py.in
new file mode 100644
index 0000000000000..dd5c075b5f112
--- /dev/null
+++ b/openmp/runtime/test/Unit/lit.site.cfg.py.in
@@ -0,0 +1,8 @@
+@AUTO_GEN_COMMENT@
+
+config.openmp_unittests_dir = "@CMAKE_CURRENT_BINARY_DIR@/../unittests"
+config.llvm_build_mode = lit_config.substitute("@LLVM_BUILD_MODE@")
+
+# Let the main config do the real work.
+lit_config.load_config(config, "@CMAKE_CURRENT_SOURCE_DIR@/../test/Unit/lit.cfg.py")
+
diff --git a/openmp/runtime/unittests/CMakeLists.txt b/openmp/runtime/unittests/CMakeLists.txt
new file mode 100644
index 0000000000000..3c56512bcf120
--- /dev/null
+++ b/openmp/runtime/unittests/CMakeLists.txt
@@ -0,0 +1,76 @@
+add_custom_target(OpenMPUnitTests)
+set_target_properties(OpenMPUnitTests PROPERTIES FOLDER "OpenMP/Tests")
+
+if(WIN32 OR STUBS_LIBRARY)
+  message(WARNING "OpenMP unittests disabled due to stub library or Windows")
+  return()
+endif()
+
+# Build a testing version of libomp that exports all symbols for unit tests.
+# This library uses the same compiled objects as libomp, but with all symbols
+# exported to allow testing internal functions.
+
+libomp_get_ldflags(LIBOMP_TEST_LDFLAGS)
+libomp_get_libflags(LIBOMP_TEST_LIBFLAGS)
+# Replace the libomp exports with the test exports exporting all symbols.
+if(LIBOMP_HAVE_VERSION_SCRIPT_FLAG)
+  string(REPLACE "${LIBOMP_SRC_DIR}/exports_so.txt"
+                  "${LIBOMP_SRC_DIR}/exports_test_so.txt"
+                  LIBOMP_TEST_LDFLAGS "${LIBOMP_TEST_LDFLAGS}")
+endif()
+# Duplicate setting of LIBOMP_LINKER_LANGUAGE to match libomp.
+if(NOT ${LIBOMP_USE_STDCPPLIB})
+  set(LIBOMP_LINKER_LANGUAGE C)
+  set(CMAKE_CXX_IMPLICIT_LINK_LIBRARIES)
+else()
+  set(LIBOMP_LINKER_LANGUAGE CXX)
+endif()
+
+# Create the testing library from the same objects as libomp.
+add_library(omp_testing SHARED $<TARGET_OBJECTS:obj.omp>)
+set_property(TARGET omp_testing PROPERTY FOLDER "OpenMP/Libraries")
+target_link_libraries(omp_testing PUBLIC default_gtest)
+target_link_libraries(omp_testing PUBLIC ${LIBOMP_TEST_LIBFLAGS} ${LIBOMP_DL_LIBS})
+set_target_properties(omp_testing PROPERTIES
+  PREFIX "" SUFFIX "" OUTPUT_NAME "libomp_testing${LIBOMP_LIBRARY_SUFFIX}"
+  LINK_FLAGS "${LIBOMP_TEST_LDFLAGS}"
+  LINKER_LANGUAGE ${LIBOMP_LINKER_LANGUAGE}
+  EXCLUDE_FROM_ALL TRUE  # Don't build by default, only when tests need it
+)
+target_include_directories(omp_testing PUBLIC
+  ${LIBOMP_INCLUDE_DIR}
+  ${LIBOMP_SRC_DIR}
+)
+
+# Make the targets default_gtest and default_gtest_main available.
+build_gtest()
+
+function(add_openmp_unittest test_name)
+  add_unittest(OpenMPUnitTests ${test_name} ${ARGN})
+
+  # Link against the testing library which exports all symbols.
+  target_link_libraries(${test_name} PRIVATE omp_testing)
+
+  if(TARGET default_gtest)
+    target_link_libraries(${test_name} PRIVATE default_gtest_main default_gtest)
+  else ()
+    target_link_libraries(${test_name} PRIVATE llvm_gtest_main llvm_gtest)
+  endif ()
+endfunction()
+
+configure_lit_site_cfg(
+  ${CMAKE_CURRENT_SOURCE_DIR}/../test/Unit/lit.site.cfg.py.in
+  ${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg.py
+  MAIN_CONFIG
+  ${CMAKE_CURRENT_SOURCE_DIR}/../test/Unit/lit.cfg.py
+)
+
+add_openmp_testsuite(
+  check-libomp-unit
+  "Running libomp unit tests"
+  ${CMAKE_CURRENT_BINARY_DIR}
+  EXCLUDE_FROM_CHECK_ALL
+  DEPENDS OpenMPUnitTests
+)
+
+add_subdirectory(String)
diff --git a/openmp/runtime/unittests/README.md b/openmp/runtime/unittests/README.md
new file mode 100644
index 0000000000000..974f877654776
--- /dev/null
+++ b/openmp/runtime/unittests/README.md
@@ -0,0 +1,9 @@
+# libomp Unit Tests
+
+Usage:
+```
+cd <your-llvm-build-directory>/runtimes/runtimes-bins
+ninja check-libomp-unit
+```
+
+Note: unit tests are currently not supported on Windows
diff --git a/openmp/runtime/unittests/String/CMakeLists.txt b/openmp/runtime/unittests/String/CMakeLists.txt
new file mode 100644
index 0000000000000..be072c76a10a6
--- /dev/null
+++ b/openmp/runtime/unittests/String/CMakeLists.txt
@@ -0,0 +1,3 @@
+add_openmp_unittest(StringTests
+  TestKmpStr.cpp
+)
diff --git a/openmp/runtime/unittests/String/TestKmpStr.cpp b/openmp/runtime/unittests/String/TestKmpStr.cpp
new file mode 100644
index 0000000000000..a22a729da9272
--- /dev/null
+++ b/openmp/runtime/unittests/String/TestKmpStr.cpp
@@ -0,0 +1,239 @@
+//===- TestKmpStr.cpp - Tests for kmp_str utilities ----------------------===//
+//
+// 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 "kmp_str.h"
+#include "gtest/gtest.h"
+#include <cstring>
+
+namespace {
+
+// Test basic string buffer initialization
+TEST(KmpStrTest, BufferInit) {
+  kmp_str_buf_t buffer;
+  __kmp_str_buf_init(&buffer);
+
+  EXPECT_NE(buffer.str, nullptr);
+  EXPECT_GT(buffer.size, 0u);
+  EXPECT_EQ(buffer.used, 0);
+  EXPECT_EQ(buffer.str[0], '\0');
+}
+
+// Test string buffer clear
+TEST(KmpStrTest, BufferClear) {
+  kmp_str_buf_t buffer;
+  __kmp_str_buf_init(&buffer);
+  __kmp_str_buf_print(&buffer, "test string");
+
+  EXPECT_GT(buffer.used, 0);
+
+  __kmp_str_buf_clear(&buffer);
+  EXPECT_EQ(buffer.used, 0);
+  EXPECT_EQ(buffer.str[0], '\0');
+
+  __kmp_str_buf_free(&buffer);
+}
+
+// Test string buffer print
+TEST(KmpStrTest, BufferPrint) {
+  kmp_str_buf_t buffer;
+  __kmp_str_buf_init(&buffer);
+
+  __kmp_str_buf_print(&buffer, "Hello, %s!", "World");
+
+  EXPECT_STREQ(buffer.str, "Hello, World!");
+  EXPECT_EQ(buffer.used, 13);
+
+  __kmp_str_buf_free(&buffer);
+}
+
+// Test string buffer concatenation
+TEST(KmpStrTest, BufferCat) {
+  kmp_str_buf_t buffer;
+  __kmp_str_buf_init(&buffer);
+
+  __kmp_str_buf_cat(&buffer, "Hello", 5);
+  __kmp_str_buf_cat(&buffer, " ", 1);
+  __kmp_str_buf_cat(&buffer, "World", 5);
+
+  EXPECT_STREQ(buffer.str, "Hello World");
+
+  __kmp_str_buf_free(&buffer);
+}
+
+// Test string buffer reservation
+TEST(KmpStrTest, BufferReserve) {
+  kmp_str_buf_t buffer;
+  __kmp_str_buf_init(&buffer);
+
+  size_t large_size = 2048;
+  __kmp_str_buf_reserve(&buffer, large_size);
+
+  EXPECT_GE(buffer.size, large_size);
+
+  __kmp_str_buf_free(&buffer);
+}
+
+// Test basic string to int conversion
+TEST(KmpStrTest, BasicStrToInt) {
+  EXPECT_EQ(__kmp_basic_str_to_int("0"), 0);
+  EXPECT_EQ(__kmp_basic_str_to_int("1"), 1);
+  EXPECT_EQ(__kmp_basic_str_to_int("42"), 42);
+  EXPECT_EQ(__kmp_basic_str_to_int("123"), 123);
+}
+
+// Test string match
+TEST(KmpStrTest, StrMatch) {
+  const char *data = "Hello World";
+
+  // Test exact match (len == 0)
+  EXPECT_TRUE(__kmp_str_match("Hello World", 0, data));
+  EXPECT_FALSE(__kmp_str_match("Hello", 0, data)); // Not exact (data is longer)
+
+  // Test prefix match (len < 0)
+  EXPECT_TRUE(
+      __kmp_str_match("Hello", -1, data)); // "Hello" is prefix of "Hello World"
+  EXPECT_FALSE(__kmp_str_match("World", -1, data)); // "World" is not a prefix
+
+  // Test minimum length match (len > 0)
+  EXPECT_TRUE(__kmp_str_match("Hello", 5, data)); // At least 5 chars match
+  EXPECT_TRUE(__kmp_str_match("Hello", 3, data)); // At least 3 chars match
+  EXPECT_FALSE(__kmp_str_match("World", 5, data)); // First chars don't match
+}
+
+// Test string contains
+TEST(KmpStrTest, StrContains) {
+  const char *data = "Hello World";
+
+  EXPECT_TRUE(__kmp_str_contains("Hello", 5, data));
+  EXPECT_TRUE(__kmp_str_contains("World", 5, data));
+  EXPECT_TRUE(__kmp_str_contains("lo Wo", 5, data));
+  EXPECT_FALSE(__kmp_str_contains("Goodbye", 7, data));
+}
+
+// Test string match for true/false values
+TEST(KmpStrTest, MatchBool) {
+  // Test true values
+  EXPECT_TRUE(__kmp_str_match_true("true"));
+  EXPECT_TRUE(__kmp_str_match_true("TRUE"));
+  EXPECT_TRUE(__kmp_str_match_true("on"));
+  EXPECT_TRUE(__kmp_str_match_true("ON"));
+  EXPECT_TRUE(__kmp_str_match_true("1"));
+  EXPECT_TRUE(__kmp_str_match_true("yes"));
+  EXPECT_TRUE(__kmp_str_match_true("YES"));
+
+  // Test false values
+  EXPECT_TRUE(__kmp_str_match_false("false"));
+  EXPECT_TRUE(__kmp_str_match_false("FALSE"));
+  EXPECT_TRUE(__kmp_str_match_false("off"));
+  EXPECT_TRUE(__kmp_str_match_false("OFF"));
+  EXPECT_TRUE(__kmp_str_match_false("0"));
+  EXPECT_TRUE(__kmp_str_match_false("no"));
+  EXPECT_TRUE(__kmp_str_match_false("NO"));
+}
+
+// Test string replace
+TEST(KmpStrTest, StrReplace) {
+  char str[] = "Hello World";
+  __kmp_str_replace(str, ' ', '_');
+  EXPECT_STREQ(str, "Hello_World");
+
+  __kmp_str_replace(str, 'o', '0');
+  EXPECT_STREQ(str, "Hell0_W0rld");
+}
+
+// Test string split
+TEST(KmpStrTest, StrSplit) {
+  char str[] = "key=value";
+  char *head = nullptr;
+  char *tail = nullptr;
+
+  __kmp_str_split(str, '=', &head, &tail);
+
+  EXPECT_STREQ(head, "key");
+  EXPECT_STREQ(tail, "value");
+}
+
+// Test file name parsing
+TEST(KmpStrTest, FileNameInit) {
+  const char *path = "/path/to/file.txt";
+  kmp_str_fname_t fname;
+  __kmp_str_fname_init(&fname, path);
+
+  EXPECT_NE(fname.path, nullptr);
+  EXPECT_STREQ(fname.path, path);
+  EXPECT_NE(fname.base, nullptr);
+  EXPECT_STREQ(fname.base, "file.txt");
+
+  __kmp_str_fname_free(&fname);
+}
+
+// Test string format
+TEST(KmpStrTest, StrFormat) {
+  char *result = __kmp_str_format("Number: %d, String: %s", 42, "test");
+
+  EXPECT_NE(result, nullptr);
+  EXPECT_STREQ(result, "Number: 42, String: test");
+
+  __kmp_str_free(&result);
+  EXPECT_EQ(result, nullptr);
+}
+
+// Test string buffer concatenate buffers
+TEST(KmpStrTest, BufferCatBuf) {
+  kmp_str_buf_t buf1, buf2;
+  __kmp_str_buf_init(&buf1);
+  __kmp_str_buf_init(&buf2);
+
+  __kmp_str_buf_print(&buf1, "Hello");
+  __kmp_str_buf_print(&buf2, " World");
+
+  __kmp_str_buf_catbuf(&buf1, &buf2);
+
+  EXPECT_STREQ(buf1.str, "Hello World");
+
+  __kmp_str_buf_free(&buf1);
+  __kmp_str_buf_free(&buf2);
+}
+
+// Test size string parsing
+TEST(KmpStrTest, StrToSize) {
+  size_t result;
+  const char *error = nullptr;
+
+  __kmp_str_to_size("100", &result, 1, &error);
+  EXPECT_EQ(error, nullptr);
+  EXPECT_EQ(result, 100u);
+
+  __kmp_str_to_size("1K", &result, 1024, &error);
+  EXPECT_EQ(error, nullptr);
+  EXPECT_EQ(result, 1024u);
+
+  __kmp_str_to_size("2M", &result, 1024, &error);
+  EXPECT_EQ(error, nullptr);
+  EXPECT_EQ(result, 2u * 1024u * 1024u);
+}
+
+// Test uint string parsing
+TEST(KmpStrTest, StrToUint) {
+  kmp_uint64 result;
+  const char *error = nullptr;
+
+  __kmp_str_to_uint("0", &result, &error);
+  EXPECT_EQ(error, nullptr);
+  EXPECT_EQ(result, 0u);
+
+  __kmp_str_to_uint("42", &result, &error);
+  EXPECT_EQ(error, nullptr);
+  EXPECT_EQ(result, 42u);
+
+  __kmp_str_to_uint("1234567890", &result, &error);
+  EXPECT_EQ(error, nullptr);
+  EXPECT_EQ(result, 1234567890u);
+}
+
+} // namespace