diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index fee18d22c7..0750f95e63 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -486,6 +486,175 @@ jobs:
           cd ../boost-root/__build__
           cmake --build . --target tests
 
+  posix-cmake-subdir:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: ubuntu-22.04
+          - os: ubuntu-24.04
+          - os: macos-15
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Use library with add_subdirectory (header-only)
+        run: |
+          cd test/cmake_subdir_test
+          mkdir __build__ && cd __build__
+          cmake ..
+          cmake --build .
+          ctest --output-on-failure --no-tests=error
+
+  posix-cmake-subdir-legacy:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: ubuntu-22.04
+          - os: ubuntu-24.04
+          - os: macos-15
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Boost
+        run: |
+          echo GITHUB_REPOSITORY: $GITHUB_REPOSITORY
+          LIBRARY=${GITHUB_REPOSITORY#*/}
+          echo LIBRARY: $LIBRARY
+          echo "LIBRARY=$LIBRARY" >> $GITHUB_ENV
+          echo GITHUB_BASE_REF: $GITHUB_BASE_REF
+          echo GITHUB_REF: $GITHUB_REF
+          REF=${GITHUB_BASE_REF:-$GITHUB_REF}
+          REF=${REF#refs/heads/}
+          echo REF: $REF
+          BOOST_BRANCH=develop && [ "$REF" == "master" ] && BOOST_BRANCH=master || true
+          echo BOOST_BRANCH: $BOOST_BRANCH
+          cd ..
+          git clone -b $BOOST_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          mkdir -p libs/$LIBRARY
+          cp -r $GITHUB_WORKSPACE/* libs/$LIBRARY
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" $LIBRARY
+
+      - name: Use library with add_subdirectory (legacy compiled)
+        run: |
+          cd ../boost-root/libs/$LIBRARY/test/cmake_subdir_test_legacy
+          mkdir __build__ && cd __build__
+          cmake ..
+          cmake --build .
+          ctest --output-on-failure --no-tests=error
+
+  posix-cmake-install:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: macos-15
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Boost
+        run: |
+          echo GITHUB_REPOSITORY: $GITHUB_REPOSITORY
+          LIBRARY=${GITHUB_REPOSITORY#*/}
+          echo LIBRARY: $LIBRARY
+          echo "LIBRARY=$LIBRARY" >> $GITHUB_ENV
+          echo GITHUB_BASE_REF: $GITHUB_BASE_REF
+          echo GITHUB_REF: $GITHUB_REF
+          REF=${GITHUB_BASE_REF:-$GITHUB_REF}
+          REF=${REF#refs/heads/}
+          echo REF: $REF
+          BOOST_BRANCH=develop && [ "$REF" == "master" ] && BOOST_BRANCH=master || true
+          echo BOOST_BRANCH: $BOOST_BRANCH
+          cd ..
+          git clone -b $BOOST_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          mkdir -p libs/$LIBRARY
+          cp -r $GITHUB_WORKSPACE/* libs/$LIBRARY
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" $LIBRARY
+
+      - name: Configure
+        run: |
+          cd ../boost-root
+          mkdir __build__ && cd __build__
+          cmake -DBOOST_INCLUDE_LIBRARIES=$LIBRARY -DCMAKE_INSTALL_PREFIX=~/.local ..
+
+      - name: Install
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target install
+
+      - name: Use the installed library (header-only)
+        run: |
+          cd ../boost-root/libs/$LIBRARY/test/cmake_install_test
+          mkdir __build__ && cd __build__
+          cmake -DCMAKE_INSTALL_PREFIX=~/.local ..
+          cmake --build .
+          ctest --output-on-failure --no-tests=error
+
+  posix-cmake-install-legacy:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: macos-15
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Boost
+        run: |
+          echo GITHUB_REPOSITORY: $GITHUB_REPOSITORY
+          LIBRARY=${GITHUB_REPOSITORY#*/}
+          echo LIBRARY: $LIBRARY
+          echo "LIBRARY=$LIBRARY" >> $GITHUB_ENV
+          echo GITHUB_BASE_REF: $GITHUB_BASE_REF
+          echo GITHUB_REF: $GITHUB_REF
+          REF=${GITHUB_BASE_REF:-$GITHUB_REF}
+          REF=${REF#refs/heads/}
+          echo REF: $REF
+          BOOST_BRANCH=develop && [ "$REF" == "master" ] && BOOST_BRANCH=master || true
+          echo BOOST_BRANCH: $BOOST_BRANCH
+          cd ..
+          git clone -b $BOOST_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          mkdir -p libs/$LIBRARY
+          cp -r $GITHUB_WORKSPACE/* libs/$LIBRARY
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" $LIBRARY
+
+      - name: Configure
+        run: |
+          cd ../boost-root
+          mkdir __build__ && cd __build__
+          cmake -DBOOST_INCLUDE_LIBRARIES=$LIBRARY -DBOOST_MATH_BUILD_WITH_LEGACY_FUNCTIONS=ON -DCMAKE_INSTALL_PREFIX=~/.local ..
+
+      - name: Install
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target install
+
+      - name: Use the installed library (legacy compiled)
+        run: |
+          cd ../boost-root/libs/$LIBRARY/test/cmake_install_test_legacy
+          mkdir __build__ && cd __build__
+          cmake -DCMAKE_INSTALL_PREFIX=~/.local ..
+          cmake --build .
+          ctest --output-on-failure --no-tests=error
+
   sycl-cmake-test:
     strategy:
       fail-fast: false
diff --git a/CMakeLists.txt b/CMakeLists.txt
index b789eb22aa..e2d6c055d3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -46,6 +46,128 @@ endif()
 
 target_compile_features(boost_math INTERFACE cxx_std_14)
 
+# Legacy C99/TR1 compiled libraries
+option(BOOST_MATH_BUILD_WITH_LEGACY_FUNCTIONS "Build the C99 and TR1 compiled libraries" OFF)
+
+if(BOOST_MATH_BUILD_WITH_LEGACY_FUNCTIONS)
+
+include(CheckCXXSourceCompiles)
+get_target_property(_config_type Boost::config TYPE)
+if(_config_type STREQUAL "INTERFACE_LIBRARY")
+  get_target_property(_config_inc Boost::config INTERFACE_INCLUDE_DIRECTORIES)
+else()
+  set(_config_inc "")
+endif()
+set(CMAKE_REQUIRED_INCLUDES "${CMAKE_CURRENT_SOURCE_DIR}/include" ${_config_inc})
+check_cxx_source_compiles("#include <${CMAKE_CURRENT_SOURCE_DIR}/config/has_long_double_support.cpp> \n int main() { return 0;}" BOOST_MATH_HAS_LONG_DOUBLE)
+unset(CMAKE_REQUIRED_INCLUDES)
+
+set(C99_SOURCES
+  acosh
+  asinh
+  atanh
+  cbrt
+  copysign
+  erfc
+  erf
+  expm1
+  fmax
+  fmin
+  fpclassify
+  hypot
+  lgamma
+  llround
+  log1p
+  lround
+  nextafter
+  nexttoward
+  round
+  tgamma
+  trunc
+)
+
+set(TR1_SOURCES
+  assoc_laguerre
+  assoc_legendre
+  beta
+  comp_ellint_1
+  comp_ellint_2
+  comp_ellint_3
+  cyl_bessel_i
+  cyl_bessel_j
+  cyl_bessel_k
+  cyl_neumann
+  ellint_1
+  ellint_2
+  ellint_3
+  expint
+  hermite
+  laguerre
+  legendre
+  riemann_zeta
+  sph_bessel
+  sph_legendre
+  sph_neumann
+)
+
+list(TRANSFORM C99_SOURCES PREPEND "src/tr1/")
+list(TRANSFORM TR1_SOURCES PREPEND "src/tr1/")
+
+list(TRANSFORM C99_SOURCES APPEND "f.cpp" OUTPUT_VARIABLE C99_SOURCESf)
+list(TRANSFORM TR1_SOURCES APPEND "f.cpp" OUTPUT_VARIABLE TR1_SOURCESf)
+
+set(types "" f)
+
+if(BOOST_MATH_HAS_LONG_DOUBLE)
+  list(TRANSFORM C99_SOURCES APPEND "l.cpp" OUTPUT_VARIABLE C99_SOURCESl)
+  list(TRANSFORM TR1_SOURCES APPEND "l.cpp" OUTPUT_VARIABLE TR1_SOURCESl)
+  list(APPEND types l)
+endif()
+
+list(TRANSFORM C99_SOURCES APPEND ".cpp")
+list(TRANSFORM TR1_SOURCES APPEND ".cpp")
+
+foreach(type IN LISTS types)
+  add_library(boost_math_tr1${type} ${TR1_SOURCES${type}})
+  add_library(Boost::math_tr1${type} ALIAS boost_math_tr1${type})
+  target_link_libraries(boost_math_tr1${type} PUBLIC Boost::config)
+  target_include_directories(boost_math_tr1${type} PRIVATE src/tr1)
+  target_include_directories(boost_math_tr1${type} PRIVATE include)
+
+  add_library(boost_math_c99${type} ${C99_SOURCES${type}})
+  add_library(Boost::math_c99${type} ALIAS boost_math_c99${type})
+  target_link_libraries(boost_math_c99${type} PUBLIC Boost::config)
+  target_include_directories(boost_math_c99${type} PRIVATE src/tr1)
+  target_include_directories(boost_math_c99${type} PRIVATE include)
+
+  if(BUILD_SHARED_LIBS)
+    target_compile_definitions(boost_math_tr1${type} PUBLIC BOOST_MATH_TR1_DYN_LINK=1)
+    target_compile_definitions(boost_math_c99${type} PUBLIC BOOST_MATH_TR1_DYN_LINK=1)
+    if(MSVC)
+      target_compile_definitions(boost_math_tr1${type} PRIVATE "BOOST_SYMBOL_EXPORT=__declspec(dllexport)" BOOST_ALL_NO_LIB)
+      target_compile_definitions(boost_math_c99${type} PRIVATE "BOOST_SYMBOL_EXPORT=__declspec(dllexport)" BOOST_ALL_NO_LIB)
+    endif()
+  endif()
+
+  target_compile_features(boost_math_tr1${type} PUBLIC cxx_std_14)
+  target_compile_features(boost_math_c99${type} PUBLIC cxx_std_14)
+
+  if(APPLE)
+    target_compile_definitions(boost_math_tr1${type} PRIVATE _DARWIN_C_SOURCE)
+    target_compile_definitions(boost_math_c99${type} PRIVATE _DARWIN_C_SOURCE)
+  endif()
+endforeach()
+
+if(BOOST_SUPERPROJECT_VERSION AND NOT CMAKE_VERSION VERSION_LESS 3.13)
+  set(boost_math_legacy_targets "")
+  foreach(type IN LISTS types)
+    list(APPEND boost_math_legacy_targets boost_math_c99${type} boost_math_tr1${type})
+  endforeach()
+  boost_install(TARGETS ${boost_math_legacy_targets} VERSION "${BOOST_SUPERPROJECT_VERSION}")
+endif()
+
+endif()
+
 if(BUILD_TESTING AND EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/test/CMakeLists.txt")
 
   add_subdirectory(test)
diff --git a/test/cmake_install_test/CMakeLists.txt b/test/cmake_install_test/CMakeLists.txt
new file mode 100644
index 0000000000..010d5e9fe3
--- /dev/null
+++ b/test/cmake_install_test/CMakeLists.txt
@@ -0,0 +1,17 @@
+# Copyright 2025 Matt Borland
+# Distributed under the Boost Software License, Version 1.0.
+# https://www.boost.org/LICENSE_1_0.txt
+
+cmake_minimum_required(VERSION 3.8...3.16)
+
+project(cmake_install_test LANGUAGES CXX)
+
+find_package(boost_math REQUIRED)
+
+add_executable(quick ../quick.cpp)
+target_link_libraries(quick Boost::math)
+
+enable_testing()
+add_test(quick quick)
+
+add_custom_target(check COMMAND ${CMAKE_CTEST_COMMAND} --output-on-failure -C $<CONFIG>)
diff --git a/test/cmake_install_test_legacy/CMakeLists.txt b/test/cmake_install_test_legacy/CMakeLists.txt
new file mode 100644
index 0000000000..b5db787104
--- /dev/null
+++ b/test/cmake_install_test_legacy/CMakeLists.txt
@@ -0,0 +1,19 @@
+# Copyright 2025 Matt Borland
+# Distributed under the Boost Software License, Version 1.0.
+# https://www.boost.org/LICENSE_1_0.txt
+
+cmake_minimum_required(VERSION 3.8...3.16)
+
+project(cmake_install_test_legacy LANGUAGES CXX)
+
+find_package(boost_math REQUIRED)
+find_package(boost_math_c99 REQUIRED)
+find_package(boost_math_tr1 REQUIRED)
+
+add_executable(quick_tr1 ../quick_tr1.cpp)
+target_link_libraries(quick_tr1 Boost::math Boost::math_c99 Boost::math_tr1)
+
+enable_testing()
+add_test(quick_tr1 quick_tr1)
+
+add_custom_target(check COMMAND ${CMAKE_CTEST_COMMAND} --output-on-failure -C $<CONFIG>)
diff --git a/test/cmake_subdir_test/CMakeLists.txt b/test/cmake_subdir_test/CMakeLists.txt
new file mode 100644
index 0000000000..09d57446d7
--- /dev/null
+++ b/test/cmake_subdir_test/CMakeLists.txt
@@ -0,0 +1,18 @@
+# Copyright 2025 Matt Borland
+# Distributed under the Boost Software License, Version 1.0.
+# https://www.boost.org/LICENSE_1_0.txt
+
+cmake_minimum_required(VERSION 3.8...3.20)
+
+project(cmake_subdir_test LANGUAGES CXX)
+
+# Math is header-only and standalone by default (no deps needed)
+add_subdirectory(../.. boostorg/math)
+
+add_executable(quick ../quick.cpp)
+target_link_libraries(quick Boost::math)
+
+enable_testing()
+add_test(quick quick)
+
+add_custom_target(check COMMAND ${CMAKE_CTEST_COMMAND} --output-on-failure -C $<CONFIG>)
diff --git a/test/cmake_subdir_test_legacy/CMakeLists.txt b/test/cmake_subdir_test_legacy/CMakeLists.txt
new file mode 100644
index 0000000000..c606705fa0
--- /dev/null
+++ b/test/cmake_subdir_test_legacy/CMakeLists.txt
@@ -0,0 +1,23 @@
+# Copyright 2025 Matt Borland
+# Distributed under the Boost Software License, Version 1.0.
+# https://www.boost.org/LICENSE_1_0.txt
+
+cmake_minimum_required(VERSION 3.8...3.20)
+
+project(cmake_subdir_test_legacy LANGUAGES CXX)
+
+# config must be added before math (compiled targets depend on Boost::config)
+add_subdirectory(../../../config boostorg/config)
+
+# Enable legacy compiled targets before adding math
+set(BOOST_MATH_BUILD_WITH_LEGACY_FUNCTIONS ON CACHE BOOL "" FORCE)
+
+add_subdirectory(../.. boostorg/math)
+
+add_executable(quick_tr1 ../quick_tr1.cpp)
+target_link_libraries(quick_tr1 Boost::math Boost::math_c99 Boost::math_tr1)
+
+enable_testing()
+add_test(quick_tr1 quick_tr1)
+
+add_custom_target(check COMMAND ${CMAKE_CTEST_COMMAND} --output-on-failure -C $<CONFIG>)
diff --git a/test/quick.cpp b/test/quick.cpp
new file mode 100644
index 0000000000..30ac1b896b
--- /dev/null
+++ b/test/quick.cpp
@@ -0,0 +1,17 @@
+// Copyright 2026 Matt Borland
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/math/special_functions/gamma.hpp>
+#include <cstdlib>
+
+int main()
+{
+    auto result = boost::math::tgamma(2.0);
+    // tgamma(2) == 1! == 1.0
+    if (result < 0.99 || result > 1.01)
+    {
+        return EXIT_FAILURE;
+    }
+    return EXIT_SUCCESS;
+}
diff --git a/test/quick_tr1.cpp b/test/quick_tr1.cpp
new file mode 100644
index 0000000000..33e21a1495
--- /dev/null
+++ b/test/quick_tr1.cpp
@@ -0,0 +1,26 @@
+// Copyright 2026 Matt Borland
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/math/tr1.hpp>
+#include <cstdlib>
+
+int main()
+{
+    // boost_cbrt from boost_math_c99
+    auto cbrt_result = boost::math::tr1::boost_cbrt(8.0);
+    if (cbrt_result < 1.99 || cbrt_result > 2.01)
+    {
+        return EXIT_FAILURE;
+    }
+
+    // boost_riemann_zeta from boost_math_tr1
+    // zeta(2) == pi^2/6 ~= 1.6449
+    auto zeta_result = boost::math::tr1::boost_riemann_zeta(2.0);
+    if (zeta_result < 1.64 || zeta_result > 1.65)
+    {
+        return EXIT_FAILURE;
+    }
+
+    return EXIT_SUCCESS;
+}