diff --git a/.github/workflows/ci-cell.yml b/.github/workflows/ci-cell.yml
index be6b8846..0aea2583 100644
--- a/.github/workflows/ci-cell.yml
+++ b/.github/workflows/ci-cell.yml
@@ -23,6 +23,10 @@ on:
         required: false
         type: boolean
         default: false
+      with-atl:
+        required: false
+        type: boolean
+        default: false
       with-mfc:
         required: false
         type: boolean
@@ -70,6 +74,7 @@ jobs:
 
           if [ "${{ inputs.c-compiler }}" = "cl" ]; then
             cmake -S "$STLSRC" -B "$STLINSTALL" \
+              -DCMAKE_DISABLE_FIND_PACKAGE_ATL=TRUE \
               -DCMAKE_DISABLE_FIND_PACKAGE_MFC=TRUE \
               -DCMAKE_INSTALL_PREFIX="$DEPS" \
               -DBUILD_EXAMPLES=OFF \
@@ -104,6 +109,7 @@ jobs:
 
           if [ "${{ inputs.c-compiler }}" = "cl" ]; then
             cmake -S "$XTSRC" -B "$XTBUILD" \
+              -DCMAKE_DISABLE_FIND_PACKAGE_ATL=TRUE \
               -DCMAKE_DISABLE_FIND_PACKAGE_MFC=TRUE \
               -DCMAKE_INSTALL_PREFIX="$DEPS" \
               -DCMAKE_PREFIX_PATH="$DEPS" \
@@ -149,8 +155,14 @@ jobs:
           else
             ACE_FLAG="-DNO_ACE=ON"
           fi
-          # Default MSVC cells suppress MFC discovery (keeps non-MFC cells lean).
-          # **with-mfc** cells leave FindMFC enabled so **MFCSTL** tests build.
+          # Default MSVC cells suppress ATL/MFC discovery (keeps lean cells lean).
+          # **with-atl** / **with-mfc** leave the matching find enabled so
+          # **ATLSTL** / **MFCSTL** can build (versions smoke; mfcstl tests).
+          if [ "${{ inputs.c-compiler }}" = "cl" ] && [ "${{ inputs.with-atl }}" != "true" ]; then
+            ATL_FLAG="-DCMAKE_DISABLE_FIND_PACKAGE_ATL=TRUE"
+          else
+            ATL_FLAG=""
+          fi
           if [ "${{ inputs.c-compiler }}" = "cl" ] && [ "${{ inputs.with-mfc }}" != "true" ]; then
             MFC_FLAG="-DCMAKE_DISABLE_FIND_PACKAGE_MFC=TRUE"
           else
@@ -158,6 +170,7 @@ jobs:
           fi
           if [ "${{ inputs.c-compiler }}" = "cl" ]; then
             cmake -B build -S . \
+              $ATL_FLAG \
               $MFC_FLAG \
               -DCMAKE_PREFIX_PATH="${RUNNER_TEMP}/sis-deps" \
               -DBUILD_EXAMPLES=ON \
@@ -207,6 +220,21 @@ jobs:
           echo "ACE_LIBRARY=${ACE_LIB}"
           echo "ACE_INCLUDE_DIR=${ACE_INC}"
 
+      - name: Verify ATL discovered
+        if: inputs.with-atl
+        shell: bash
+        run: |
+          set -euo pipefail
+          ATL_HAVE="$(grep -E '^ATL_HAVE_ATL:(BOOL|INTERNAL)=' build/CMakeCache.txt | head -1 | cut -d= -f2- || true)"
+          ATL_FOUND="$(grep -E '^ATL_FOUND:(BOOL|INTERNAL|STRING)=' build/CMakeCache.txt | head -1 | cut -d= -f2- || true)"
+          if [ "${ATL_HAVE}" != "1" ] && [ "${ATL_HAVE}" != "TRUE" ] && [ "${ATL_HAVE}" != "ON" ] && [ "${ATL_FOUND}" != "YES" ] && [ "${ATL_FOUND}" != "TRUE" ] && [ "${ATL_FOUND}" != "ON" ]; then
+            echo "with-atl requested but ATL was not found:" >&2
+            grep -i '^ATL_' build/CMakeCache.txt || true
+            exit 1
+          fi
+          echo "ATL_HAVE_ATL=${ATL_HAVE}"
+          echo "ATL_FOUND=${ATL_FOUND}"
+
       - name: Verify MFC discovered
         if: inputs.with-mfc
         shell: bash
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 75493e90..666e8100 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -63,6 +63,7 @@ jobs:
       cpp-compiler: ${{ matrix.cpp_compiler }}
       build-type: Release
       with-ace: false
+      with-atl: false
       with-mfc: false
     secrets: inherit
 
@@ -84,6 +85,29 @@ jobs:
       cpp-compiler: ${{ matrix.cpp_compiler }}
       build-type: Release
       with-ace: true
+      with-atl: false
+      with-mfc: false
+    secrets: inherit
+
+  cell-atl:
+    name: CI ATL (${{ matrix.id }})
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - id: windows-cl-atl
+            os: windows-latest
+            c_compiler: cl
+            cpp_compiler: cl
+    uses: ./.github/workflows/ci-cell.yml
+    with:
+      cell-id: ${{ matrix.id }}
+      os: ${{ matrix.os }}
+      c-compiler: ${{ matrix.c_compiler }}
+      cpp-compiler: ${{ matrix.cpp_compiler }}
+      build-type: Release
+      with-ace: false
+      with-atl: true
       with-mfc: false
     secrets: inherit
 
@@ -105,6 +129,7 @@ jobs:
       cpp-compiler: ${{ matrix.cpp_compiler }}
       build-type: Release
       with-ace: false
+      with-atl: false
       with-mfc: true
     secrets: inherit
 
@@ -155,6 +180,7 @@ jobs:
           set -euo pipefail
           if [ "${{ matrix.c_compiler }}" = "cl" ]; then
             cmake -B build -S . \
+              -DCMAKE_DISABLE_FIND_PACKAGE_ATL=TRUE \
               -DCMAKE_DISABLE_FIND_PACKAGE_MFC=TRUE \
               -DBUILD_EXAMPLES=OFF \
               -DBUILD_TESTING=OFF
diff --git a/CMakeLists.txt b/CMakeLists.txt
index a79785a4..02f1f520 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -95,9 +95,17 @@ endif(MSVC)
 
 if(WIN32)
 
+	find_package(ATL QUIET)
 	find_package(MFC QUIET)
 endif(WIN32)
 
+if(ATL_FOUND)
+
+	message("-- using Active Template Library")
+
+	add_compile_definitions(STLSOFT_HAS_ATL)
+endif(ATL_FOUND)
+
 if(MFC_FOUND)
 
 	# Shared MFC (/MD + _AFXDLL) unless the project is configured for the
diff --git a/TODO.md b/TODO.md
index 0d8affee..4a40c9fe 100644
--- a/TODO.md
+++ b/TODO.md
@@ -27,10 +27,12 @@
 
 ### 1.11.1
 
-* [ ] Remove **WTL**;
 * [x] ~~~ACESTL: implement `invoke_ACE_OS_snprintf` in terms of `stlsoft_C_snprintf()`~~~ - ✅;
+* [x] ~~~CI: exercise **ATLSTL** on a Windows cell~~~ - ✅;
 * [x] ~~~CI: exercise **MFCSTL** on a Windows cell (drop / gate `CMAKE_DISABLE_FIND_PACKAGE_MFC`; confirm MSVC+MFC on the runner)~~~ - ✅;
+* [ ] Remove **WTL**;
 * [ ] Resolve finally the structure and semantics of the top-level execution scripts (**run_all_unit_tests.sh**, **run_all_scratch_tests.sh**, **run_all_examples.sh**, **execute_performance_tests.sh**, and Windows `.cmd` counterparts) on all platforms — discovery globs, execute-bit / artifact restore, zero-match failure, verbosity, and CI wiring;
+* [ ] bring in some essential unit-tests from interal repo;
 
 
 ### 1.11.2
diff --git a/cmake/FindATL.cmake b/cmake/FindATL.cmake
new file mode 100644
index 00000000..2c1e71f9
--- /dev/null
+++ b/cmake/FindATL.cmake
@@ -0,0 +1,36 @@
+# FindATL.cmake
+#
+# Detects Microsoft Active Template Library (ATL) headers for MSVC on
+# Windows (not MinGW / Borland).
+#
+# Sets:
+#   ATL_FOUND
+#   ATL_HAVE_ATL   (CACHE; true when atlbase.h is usable)
+#
+# There is no stock CMake FindATL; this mirrors FindMFC's Windows-only
+# check. ATL is typically header-available with the VC ATL component and
+# needs no extra link flags for compile-only / version smoke use.
+
+
+set(ATL_FOUND FALSE)
+
+# Only attempt when the toolset has a chance of shipping atlbase.h:
+if(WIN32 AND NOT UNIX AND NOT BORLAND AND NOT MINGW)
+
+	if(NOT DEFINED ATL_HAVE_ATL)
+
+		include(CheckIncludeFileCXX)
+
+		check_include_file_cxx("atlbase.h" ATL_HAVE_ATL)
+	endif()
+
+	if(ATL_HAVE_ATL)
+
+		set(ATL_FOUND TRUE)
+	endif()
+endif()
+
+mark_as_advanced(ATL_HAVE_ATL)
+
+
+# ############################## end of file ############################# #
diff --git a/test/unit/test.unit.versions/entry.cpp b/test/unit/test.unit.versions/entry.cpp
index 4b43cf80..a5d68981 100644
--- a/test/unit/test.unit.versions/entry.cpp
+++ b/test/unit/test.unit.versions/entry.cpp
@@ -31,6 +31,9 @@
 #ifdef STLSOFT_HAS_ACE
 # include <acestl/acestl.hpp>
 #endif
+#ifdef STLSOFT_HAS_ATL
+# include <atlstl/atlstl.hpp>
+#endif
 #ifdef STLSOFT_HAS_MFC
 # include <mfcstl/mfcstl.hpp>
 #endif
@@ -58,6 +61,9 @@ namespace {
     static void TEST__STLSOFT_VER();
 #ifdef STLSOFT_HAS_ACE
     static void TEST__ACESTL_VER();
+#endif
+#ifdef STLSOFT_HAS_ATL
+    static void TEST__ATLSTL_VER();
 #endif
     static void TEST__PLATFORMSTL_VER();
 #if 0
@@ -91,6 +97,9 @@ int main(int argc, char **argv)
         XTESTS_RUN_CASE(TEST__STLSOFT_VER);
 #ifdef STLSOFT_HAS_ACE
         XTESTS_RUN_CASE(TEST__ACESTL_VER);
+#endif
+#ifdef STLSOFT_HAS_ATL
+        XTESTS_RUN_CASE(TEST__ATLSTL_VER);
 #endif
         XTESTS_RUN_CASE(TEST__PLATFORMSTL_VER);
 #if 0
@@ -132,6 +141,13 @@ static void TEST__ACESTL_VER()
     TEST_INT_EQ(_ACESTL_VER_1_2_1, _ACESTL_VER);
 }
 #endif
+#ifdef STLSOFT_HAS_ATL
+
+static void TEST__ATLSTL_VER()
+{
+    TEST_INT_EQ(_ATLSTL_VER_1_7_1, _ATLSTL_VER);
+}
+#endif
 
 static void TEST__PLATFORMSTL_VER()
 {