diff --git a/.github/actions/Build_and_Test_CppInterOp/action.yml b/.github/actions/Build_and_Test_CppInterOp/action.yml
index b97d2e8ae..caa6504d5 100644
--- a/.github/actions/Build_and_Test_CppInterOp/action.yml
+++ b/.github/actions/Build_and_Test_CppInterOp/action.yml
@@ -91,15 +91,15 @@ runs:
           echo "CLING_BUILD_DIR=$env:CLING_BUILD_DIR"
           echo "CLING_BUILD_DIR=$env:CLING_BUILD_DIR" >> $env:GITHUB_ENV
 
-          $env:CPLUS_INCLUDE_PATH="$env:CLING_DIR\tools\cling\include;$env:CLING_BUILD_DIR\include;$env:LLVM_DIR\llvm\include;$env:LLVM_DIR\clang\include;$env:LLVM_BUILD_DIR\include;$env:LLVM_BUILD_DIR\tools\clang\include;$env:PWD_DIR\include;"
-          echo "CPLUS_INCLUDE_PATH=$env:CPLUS_INCLUDE_PATH"
-          echo "CPLUS_INCLUDE_PATH=$env:CPLUS_INCLUDE_PATH" >> $env:GITHUB_ENV
+          $env:IncludePath="$env:IncludePath;$env:CLING_DIR\tools\cling\include;$env:CLING_BUILD_DIR\include;$env:LLVM_DIR\llvm\include;$env:LLVM_DIR\clang\include;$env:LLVM_BUILD_DIR\include;$env:LLVM_BUILD_DIR\tools\clang\include;$env:PWD_DIR\include;"
+          echo "IncludePath=$env:IncludePath"
+          echo "IncludePath=$env:IncludePath" >> $env:GITHUB_ENV
         }
         else
         {
-          $env:CPLUS_INCLUDE_PATH="$env:LLVM_DIR\llvm\include;$env:LLVM_DIR\clang\include;$env:LLVM_BUILD_DIR\include;$env:LLVM_BUILD_DIR\tools\clang\include;$env:PWD_DIR\include;"
-          echo "CPLUS_INCLUDE_PATH=$env:CPLUS_INCLUDE_PATH"
-          echo "CPLUS_INCLUDE_PATH=$env:CPLUS_INCLUDE_PATH" >> $env:GITHUB_ENV
+          $env:IncludePath="$env:IncludePath;$env:LLVM_DIR\llvm\include;$env:LLVM_DIR\clang\include;$env:LLVM_BUILD_DIR\include;$env:LLVM_BUILD_DIR\tools\clang\include;$env:PWD_DIR\include;"
+          echo "IncludePath=$env:IncludePath"
+          echo "IncludePath=$env:IncludePath" >> $env:GITHUB_ENV
         }
 
         $env:CB_PYTHON_DIR="$env:PWD_DIR\cppyy-backend\python"
@@ -113,7 +113,7 @@ runs:
         # Build CppInterOp next to cling and llvm-project.
         mkdir build
         cd build
-        $env:CPPINTEROP_BUILD_DIR="$env:PWD_DIR"
+        $env:CPPINTEROP_BUILD_DIR=$PWD.Path
         echo "CPPINTEROP_BUILD_DIR=$env:CPPINTEROP_BUILD_DIR"
         echo "CPPINTEROP_BUILD_DIR=$env:CPPINTEROP_BUILD_DIR" >> $env:GITHUB_ENV
         if ( "${{ matrix.cling }}" -imatch "On" )
@@ -123,14 +123,14 @@ runs:
                 -DCPPINTEROP_USE_REPL=OFF                                  `
                 -DCling_DIR="$env:LLVM_BUILD_DIR\tools\cling"   `
                 -DLLVM_DIR="$env:LLVM_BUILD_DIR" `
-                -DLLVM_ENABLE_WERROR=On                          `
+                -DLLVM_ENABLE_WERROR=On -DBUILD_SHARED_LIBS=ON `
                 -DClang_DIR="$env:LLVM_BUILD_DIR"  -DCODE_COVERAGE=${{ env.CODE_COVERAGE }} -DCMAKE_INSTALL_PREFIX="$env:CPPINTEROP_DIR"  ..\
         }
         else
         {
           cmake -DCMAKE_BUILD_TYPE=${{ env.BUILD_TYPE }}    `
                 -DLLVM_DIR="$env:LLVM_BUILD_DIR\lib\cmake\llvm"  `
-                -DLLVM_ENABLE_WERROR=On                          `
+                -DLLVM_ENABLE_WERROR=On -DBUILD_SHARED_LIBS=ON `
                 -DClang_DIR="$env:LLVM_BUILD_DIR\lib\cmake\clang"  -DCODE_COVERAGE=${{ env.CODE_COVERAGE }}  -DCMAKE_INSTALL_PREFIX="$env:CPPINTEROP_DIR"  ..\
         }
-        cmake --build . --config ${{ env.BUILD_TYPE }} --target check-cppinterop --parallel ${{ env.ncpus }}
+        cmake --build . --config ${{ env.BUILD_TYPE }} --target check-cppinterop
diff --git a/.github/actions/Build_and_Test_cppyy/action.yml b/.github/actions/Build_and_Test_cppyy/action.yml
index 244908348..8559f7392 100644
--- a/.github/actions/Build_and_Test_cppyy/action.yml
+++ b/.github/actions/Build_and_Test_cppyy/action.yml
@@ -138,3 +138,102 @@ runs:
         tail -n1 test_xfailed.log
         echo "Return Code: ${RETCODE}"
         exit $RETCODE
+
+    - name: Build and Install cppyy-backend
+      if: ${{ matrix.cppyy == 'On' && runner.os == 'Windows' }}
+      shell: powershell
+      run: |
+        # Download cppyy-backend
+        git clone --depth=1 https://github.com/compiler-research/cppyy-backend.git
+        cd cppyy-backend
+        mkdir $env:CPPINTEROP_DIR\lib
+        mkdir build
+        cd build
+        # Install CppInterOp
+        cd $env:CPPINTEROP_BUILD_DIR
+        cmake --build . --target install --parallel ${{ env.ncpus }}
+        find.exe . -name "*.dll"
+        find.exe . -name "*.lib"
+        cd ..\cppyy-backend\build\
+        # Build and Install cppyy-backend
+        cmake -DCppInterOp_DIR=$env:CPPINTEROP_DIR -DCMAKE_BUILD_TYPE=${{ env.BUILD_TYPE }} ..
+        cmake --build . --config ${{ env.BUILD_TYPE }} --parallel ${{ env.ncpus }}
+        find.exe . -name "*"
+        cp Release\libcppyy-backend.dll $env:CPPINTEROP_DIR\lib\
+        cd ..
+
+    - name: Install CPyCppyy
+      if: ${{ matrix.cppyy == 'On' && runner.os == 'Windows' }}
+      shell: powershell
+      run: |
+        python -m venv .venv
+        . .\.venv\Scripts\Activate.ps1
+        # Install CPyCppyy
+        git clone --depth=1 https://github.com/compiler-research/CPyCppyy.git
+        mkdir CPyCppyy\build
+        cd CPyCppyy\build
+        cmake ..
+        cmake --build . --parallel ${{ env.ncpus }}
+        #
+        env:CPYCPPYY_DIR = $PWD.Path
+        cd ../..
+        # We need CPYCPPYY_DIR later
+        echo "CPYCPPYY_DIR=$env:CPYCPPYY_DIR" >> $env:GITHUB_ENV
+
+    - name: Install cppyy
+      if: ${{ matrix.cppyy == 'On' && runner.os == 'Windows' }}
+      shell: powershell
+      run: |
+        # source virtual environment
+        . .\.venv\Scripts\Activate.ps1
+        # Install cppyy
+        git clone --depth=1 https://github.com/compiler-research/cppyy.git
+        cd cppyy
+        python -m pip install --upgrade . --no-deps
+        cd ..
+
+    - name: Run cppyy
+      if: ${{ matrix.cppyy == 'On' && runner.os == 'Windows' }}
+      shell: powershell
+      run: |
+        # Run cppyy
+        . .\.venv\Scripts\Activate.ps1
+        $env:PYTHONPATH=$env:PYTHONPATH:$env:CPYCPPYY_DIR:$env:CB_PYTHON_DIR
+        python -c "import cppyy"
+        # We need PYTHONPATH later
+        echo "PYTHONPATH=$env:PYTHONPATH" >> $GITHUB_ENV
+
+    - name: Run the tests
+      if: ${{ matrix.cppyy == 'On' && runner.os == 'Windows' }}
+      shell: powershell
+      run: |
+        # Run the tests
+        . .\.venv\Scripts\Activate.ps1
+        cd cppyy\test
+        echo ::group::Prepare For Testing
+        make all
+        python -m pip install --upgrade pip
+        python -m pip install pytest
+        python -m pip install pytest-xdist
+        python -m pip install numba
+        echo ::endgroup::
+        echo ::group::Run complete test suite
+        $ErrorActionPreference = "Stop"
+        python -m pytest -sv -ra 2>&1 | Tee-Object -FilePath complete_testrun.log
+        $ErrorActionPreference = "Continue"
+        echo ::group::Crashing Test Logs
+        # See if we don't have a crash that went away
+        # Comment out all xfails but the ones that have a run=False condition.
+        find.exe . -name "*.py" -exec sed.exe -i '/run=False/!s/^ *@mark.xfail\(.*\)/#&/' {} \;
+        python -m pytest -n 1 -m "xfail" --runxfail -sv -ra --max-worker-restart 512 2>&1 | Tee-Object -FilePath test_crashed.log
+        $LASTEXITCODE = 0
+        git checkout .
+        echo ::endgroup::
+        echo ::group::XFAIL Test Logs
+        # Rewrite all xfails that have a run clause to skipif. This way we will
+        # avoid conditionally crashing xfails
+        find.exe . -name "*.py" -exec sed.exe -i -E 's/(^ *)@mark.xfail\(run=(.*)/\1@mark.skipif(condition=not \2/g' {} \;
+        # See if we don't have an xfail that went away
+        python -m pytest --runxfail -sv -ra  | tee test_xfailed.log 2>&1 || true
+        git checkout .
+        echo ::endgroup::
diff --git a/.github/workflows/Windows-arm.yml b/.github/workflows/Windows-arm.yml
index 0a17ff458..7489f47bb 100644
--- a/.github/workflows/Windows-arm.yml
+++ b/.github/workflows/Windows-arm.yml
@@ -132,6 +132,8 @@ jobs:
 
     - uses: ./.github/actions/Build_and_Test_CppInterOp
 
+    - uses: ./.github/actions/Build_and_Test_cppyy
+
     - name: Setup tmate session
       if: ${{ failure() && runner.debug }}
       uses: mxschmitt/action-tmate@v3
diff --git a/.github/workflows/Windows.yml b/.github/workflows/Windows.yml
index d66e8f462..327d270bd 100644
--- a/.github/workflows/Windows.yml
+++ b/.github/workflows/Windows.yml
@@ -132,6 +132,8 @@ jobs:
 
     - uses: ./.github/actions/Build_and_Test_CppInterOp
 
+    - uses: ./.github/actions/Build_and_Test_cppyy
+
     - name: Setup tmate session
       if: ${{ failure() && runner.debug }}
       uses: mxschmitt/action-tmate@v3
diff --git a/lib/CppInterOp/CMakeLists.txt b/lib/CppInterOp/CMakeLists.txt
index 8835511b4..805209640 100644
--- a/lib/CppInterOp/CMakeLists.txt
+++ b/lib/CppInterOp/CMakeLists.txt
@@ -146,3 +146,9 @@ string(REPLACE ";" "\;" _VER CPPINTEROP_VERSION)
 set_source_files_properties(CppInterOp.cpp PROPERTIES COMPILE_DEFINITIONS
   "LLVM_BINARY_DIR=\"${LLVM_BINARY_DIR}\";CPPINTEROP_VERSION=\"${_VAR}\""
 )
+
+if(MSVC)
+  set_target_properties(clangCppInterOp PROPERTIES
+      LINK_FLAGS "/DEF:${CMAKE_CURRENT_SOURCE_DIR}/clangCppInterOp.def"
+  )
+endif()
diff --git a/lib/CppInterOp/clangCppInterOp.def b/lib/CppInterOp/clangCppInterOp.def
new file mode 100644
index 000000000..75a2de413
--- /dev/null
+++ b/lib/CppInterOp/clangCppInterOp.def
@@ -0,0 +1,66 @@
+LIBRARY clangCppInterOp
+EXPORTS
+  ?write@raw_ostream@llvm@@QEAAAEAV12@PEBD_K@Z
+  __imp_?classof@DeclContext@clang@@SA_NPEBVDecl@2@@Z
+  ?create@Interpreter@clang@@SA?AV?$Expected@V?$unique_ptr@VInterpreter@clang@@U?$default_delete@VInterpreter@clang@@@std@@@std@@@llvm@@V?$unique_ptr@VCompilerInstance@clang@@U?$default_delete@VCompilerInstance@clang@@@std@@@std@@@Z
+  ?errs@llvm@@YAAEAVraw_fd_ostream@1@XZ
+  ?DestroyDataAndMakeUninit@APValue@clang@@AEAAXXZ
+  ?dbgs@llvm@@YAAEAVraw_ostream@1@XZ
+  ?fatalUncheckedError@Error@llvm@@AEBAXXZ
+  ?logAllUnhandledErrors@llvm@@YAXVError@1@AEAVraw_ostream@1@VTwine@1@@Z
+  ?isFloatingType@Type@clang@@QEBA_NXZ
+  ?getDecl@TagType@clang@@QEBAPEAVTagDecl@2@XZ
+  ?hasDefiningAttr@Decl@clang@@QEBA_NXZ
+  ?getNumParams@FunctionDecl@clang@@QEBAIXZ
+  ?getTemplateInstantiationPattern@FunctionDecl@clang@@QEBAPEAV12@_N@Z
+  ?getTemplateSpecializationArgs@FunctionDecl@clang@@QEBAPEBVTemplateArgumentList@2@XZ
+  ?initSlowCase@APInt@llvm@@AEAAX_K_N@Z
+  ?compare@APInt@llvm@@AEBAHAEBV12@@Z
+  ?compareSigned@APInt@llvm@@AEBAHAEBV12@@Z
+  ?compareValues@APSInt@llvm@@SAHAEBV12@0@Z
+  ??1raw_ostream@llvm@@UEAA@XZ
+  ??1raw_string_ostream@llvm@@UEAA@XZ
+  ?write_impl@raw_string_ostream@llvm@@EEAAXPEBD_K@Z
+  ?changeColor@raw_ostream@llvm@@UEAAAEAV12@W4Colors@12@_N1@Z
+  ?resetColor@raw_ostream@llvm@@UEAAAEAV12@XZ
+  ?reverseColor@raw_ostream@llvm@@UEAAAEAV12@XZ
+  ?preferred_buffer_size@raw_ostream@llvm@@MEBA_KXZ
+  ?SetBufferAndMode@raw_ostream@llvm@@AEAAXPEAD_KW4BufferKind@12@@Z
+  ?flush_nonempty@raw_ostream@llvm@@AEAAXXZ
+  ?anchor@raw_ostream@llvm@@EEAAXXZ
+  ?maybeMangleDeclName@compat@@YAXAEBVGlobalDecl@clang@@AEAV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z
+  ?grow_pod@?$SmallVectorBase@I@llvm@@IEAAXPEAX_K1@Z
+  ??0APInt@llvm@@QEAA@IV?$ArrayRef@_K@1@@Z
+  ?sext@APInt@llvm@@QEBA?AV12@I@Z
+  ?zext@APInt@llvm@@QEBA?AV12@I@Z
+  ?allocate_buffer@llvm@@YAPEAX_K0@Z
+  ?RehashTable@StringMapImpl@llvm@@IEAAII@Z
+  ?LookupBucketFor@StringMapImpl@llvm@@IEAAIVStringRef@2@I@Z
+  ?hash@StringMapImpl@llvm@@SAIVStringRef@2@@Z
+  ?getUnqualifiedDesugaredType@Type@clang@@QEBAPEBV12@XZ
+  ?getASTContext@Decl@clang@@QEBAAEAVASTContext@2@XZ
+  ?getAttrs@Decl@clang@@QEBAAEBV?$SmallVector@PEAVAttr@clang@@$03@llvm@@XZ
+  ?lookup@DeclContext@clang@@QEBA?AVDeclContextLookupResult@2@VDeclarationName@2@@Z
+  ?isThisDeclarationADefinition@VarDecl@clang@@QEBA?AW4DefinitionKind@12@AEAVASTContext@2@@Z
+  ?isInjectedClassName@RecordDecl@clang@@QEBA_NXZ
+  ?getTypeDeclTypeSlow@ASTContext@clang@@AEBA?AVQualType@2@PEBVTypeDecl@2@@Z
+  ?getComplexType@ASTContext@clang@@QEBA?AVQualType@2@V32@@Z
+  ?createMangleContext@ASTContext@clang@@QEAAPEAVMangleContext@2@PEBVTargetInfo@2@@Z
+  ?getSpecializations@ClassTemplateDecl@clang@@IEBAAEAV?$FoldingSetVector@VClassTemplateSpecializationDecl@clang@@V?$SmallVector@PEAVClassTemplateSpecializationDecl@clang@@$07@llvm@@@llvm@@XZ
+  ?getSpecializedTemplate@VarTemplateSpecializationDecl@clang@@QEBAPEAVVarTemplateDecl@2@XZ
+  ?shouldMangleDeclName@MangleContext@clang@@QEAA_NPEBVNamedDecl@2@@Z
+  ?mangleName@MangleContext@clang@@QEAAXVGlobalDecl@2@AEAVraw_ostream@llvm@@@Z
+  ?getStdNamespace@Sema@clang@@QEBAPEAVNamespaceDecl@2@XZ
+  ?castToDeclContext@Decl@clang@@SAPEAVDeclContext@2@PEBV12@@Z
+  ?decls_begin@DeclContext@clang@@QEBA?AVdecl_iterator@12@XZ
+  ?classof@DeclContext@clang@@SA_NPEBVDecl@2@@Z
+  ?Parse@Interpreter@clang@@QEAA?AV?$Expected@AEAUPartialTranslationUnit@clang@@@llvm@@VStringRef@4@@Z
+  ?Execute@Interpreter@clang@@QEAA?AVError@llvm@@AEAUPartialTranslationUnit@2@@Z
+  ?getLValueReferenceType@ASTContext@clang@@QEBA?AVQualType@2@V32@_N@Z
+  ?getCompilerInstance@Interpreter@clang@@QEAAPEAVCompilerInstance@2@XZ
+  ?RunningOnValgrind@sys@llvm@@YA_NXZ
+  ?grow_pod@?$SmallVectorBase@_K@llvm@@IEAAXPEAX_K1@Z
+  ?access@fs@sys@llvm@@YA?AVerror_code@std@@AEBVTwine@3@W4AccessMode@123@@Z
+  ?CreateCpp@IncrementalCompilerBuilder@clang@@QEAA?AV?$Expected@V?$unique_ptr@VCompilerInstance@clang@@U?$default_delete@VCompilerInstance@clang@@@std@@@std@@@llvm@@XZ
+  ?getMainExecutable@fs@sys@llvm@@YA?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@PEBDPEAX@Z
+  ?parent_path@path@sys@llvm@@YA?AVStringRef@3@V43@W4Style@123@@Z