diff --git a/Common/Core/vtkConfigure.h.in b/Common/Core/vtkConfigure.h.in
index 7358c459d77..41533daeb7f 100644
--- a/Common/Core/vtkConfigure.h.in
+++ b/Common/Core/vtkConfigure.h.in
@@ -73,7 +73,7 @@
 
 /* Atomic operations */
 #cmakedefine VTK_HAVE_SYNC_BUILTINS
-#if defined(WIN32)
+#if defined(_WIN32)
  #cmakedefine VTK_HAS_INTERLOCKEDADD
 #endif
 
diff --git a/Common/Core/vtkWin32Header.h b/Common/Core/vtkWin32Header.h
index b3dc5b79f54..b4e40d0bc80 100644
--- a/Common/Core/vtkWin32Header.h
+++ b/Common/Core/vtkWin32Header.h
@@ -45,7 +45,7 @@ Do_not_include_vtkWin32Header_directly__vtkSystemIncludes_includes_it;
 
 //
 // Windows specific stuff------------------------------------------
-#if defined(_WIN32) || defined(WIN32)
+#if defined(_WIN32)
 
 // define strict header for windows
 #ifndef STRICT
diff --git a/Common/System/Testing/Cxx/otherTimerLog.cxx b/Common/System/Testing/Cxx/otherTimerLog.cxx
index fc81994a098..571703bbfff 100644
--- a/Common/System/Testing/Cxx/otherTimerLog.cxx
+++ b/Common/System/Testing/Cxx/otherTimerLog.cxx
@@ -48,7 +48,7 @@ void otherTimerLogTest(ostream& strm)
       {
       a *= a;
       }
-#ifndef WIN32
+#ifndef _WIN32
     sleep (1);
 #else
     Sleep(1000);
diff --git a/Filters/FlowPaths/vtkParticleTracerBase.cxx b/Filters/FlowPaths/vtkParticleTracerBase.cxx
index f1b96a7187c..926c2c815cc 100644
--- a/Filters/FlowPaths/vtkParticleTracerBase.cxx
+++ b/Filters/FlowPaths/vtkParticleTracerBase.cxx
@@ -133,7 +133,7 @@ vtkParticleTracerBase::vtkParticleTracerBase()
   this->SetNumberOfInputPorts(2);
 
 #ifdef JB_H5PART_PARTICLE_OUTPUT
-#ifdef WIN32
+#ifdef _WIN32
   vtkDebugMacro(<<"Setting vtkH5PartWriter");
   vtkH5PartWriter *writer = vtkH5PartWriter::New();
 #else
diff --git a/Filters/FlowPaths/vtkTemporalStreamTracer.cxx b/Filters/FlowPaths/vtkTemporalStreamTracer.cxx
index 2b6873fd369..fb194a57c09 100644
--- a/Filters/FlowPaths/vtkTemporalStreamTracer.cxx
+++ b/Filters/FlowPaths/vtkTemporalStreamTracer.cxx
@@ -46,7 +46,7 @@ PURPOSE.  See the above copyright notice for more information.
 #include "vtkToolkits.h" // For VTK_USE_MPI
 #include <cassert>
 
-#ifdef WIN32
+#ifdef _WIN32
   #undef JB_H5PART_PARTICLE_OUTPUT
 #else
 //  #define JB_H5PART_PARTICLE_OUTPUT
@@ -66,7 +66,7 @@ using namespace vtkTemporalStreamTracerNamespace;
 //----------------------------------------------------------------------------
 //#define JB_DEBUG__
 #if defined JB_DEBUG__
-  #ifdef WIN32
+  #ifdef _WIN32
       #define OUTPUTTEXT(a) vtkOutputWindowDisplayText(a);
   #else
   #endif
@@ -132,7 +132,7 @@ vtkTemporalStreamTracer::vtkTemporalStreamTracer()
   this->SetNumberOfInputPorts(2);
 
 #ifdef JB_H5PART_PARTICLE_OUTPUT
-#ifdef WIN32
+#ifdef _WIN32
   vtkDebugMacro(<<"Setting vtkH5PartWriter");
   vtkH5PartWriter *writer = vtkH5PartWriter::New();
 #else
diff --git a/Filters/StatisticsGnuR/vtkRInterface.cxx b/Filters/StatisticsGnuR/vtkRInterface.cxx
index dfc19368bc0..193b0b09777 100644
--- a/Filters/StatisticsGnuR/vtkRInterface.cxx
+++ b/Filters/StatisticsGnuR/vtkRInterface.cxx
@@ -41,7 +41,7 @@ vtkStandardNewMacro(vtkRInterface);
 #include "Rversion.h"
 #include "Rdefines.h"
 
-#ifndef WIN32
+#ifndef _WIN32
 #define CSTACK_DEFNS
 #define R_INTERFACE_PTRS
 #include "Rinterface.h"
@@ -75,7 +75,7 @@ class vtkImplementationRSingleton
     return;
     }
 
-#ifndef WIN32
+#ifndef _WIN32
     R_SignalHandlers = 0;
 #endif
 
@@ -97,7 +97,7 @@ class vtkImplementationRSingleton
           R_CStackLimit = (uintptr_t)-1;
       #endif
 
-      #ifndef WIN32
+      #ifndef _WIN32
           R_Interactive = static_cast<Rboolean>(TRUE);
       #endif
           setup_Rmainloop();
@@ -112,7 +112,7 @@ class vtkImplementationRSingleton
     rcommand.append("f<-file(paste(tempdir(), \"/Routput.txt\", sep = \"\"), open=\"wt+\")\nsink(f)\n");
     this->tmpFilePath.clear();
     this->tmpFilePath.append(R_TempDir);
-#ifdef WIN32
+#ifdef _WIN32
     this->tmpFilePath.append("\\Routput.txt");
 #else
     this->tmpFilePath.append("/Routput.txt");
diff --git a/IO/Image/Testing/Cxx/TestTIFFReaderMultiple.cxx b/IO/Image/Testing/Cxx/TestTIFFReaderMultiple.cxx
index 25f5487af57..ba00c7659eb 100644
--- a/IO/Image/Testing/Cxx/TestTIFFReaderMultiple.cxx
+++ b/IO/Image/Testing/Cxx/TestTIFFReaderMultiple.cxx
@@ -16,7 +16,7 @@
 #include <vtkSmartPointer.h>
 #include "vtkTestErrorObserver.h"
 
-#ifndef WIN32
+#ifndef _WIN32
 #include <fcntl.h>
 #endif
 
@@ -28,7 +28,7 @@ int TestTIFFReaderMultiple(int argc, char *argv[])
     return EXIT_FAILURE;
     }
 
-#ifndef WIN32
+#ifndef _WIN32
   // See how many file descriptors are in use
   int fdUsedBefore = 1;
   for (int i = 0; i < 1024; ++i)
@@ -62,7 +62,7 @@ int TestTIFFReaderMultiple(int argc, char *argv[])
     errorObserver->Clear();
     }
 
-#ifndef WIN32
+#ifndef _WIN32
   // See how many file descriptors are in use
   int fdUsedAfter = 1;
   for (int i = 0; i < 1024; ++i)
diff --git a/IO/Import/vtkVRMLImporter_Yacc.h b/IO/Import/vtkVRMLImporter_Yacc.h
index f227d7d9866..2f46b905c5b 100644
--- a/IO/Import/vtkVRMLImporter_Yacc.h
+++ b/IO/Import/vtkVRMLImporter_Yacc.h
@@ -1702,7 +1702,7 @@ void vtkVRMLYaccData::expect(int type)
 
 #define FLEX_SCANNER
 
-#ifdef WIN32
+#ifdef _WIN32
 #include <io.h>
 #else
 #include <unistd.h>
diff --git a/IO/LSDyna/private/LSDynaFamily.cxx b/IO/LSDyna/private/LSDynaFamily.cxx
index 19bf9db4464..3dcb31c7143 100644
--- a/IO/LSDyna/private/LSDynaFamily.cxx
+++ b/IO/LSDyna/private/LSDynaFamily.cxx
@@ -36,7 +36,7 @@ namespace
 // Usually stat uses 32 bit fields, and stat64 (with underscores in Windows) uses 64 bit fields.
 // But on OS X and FreeBSD, stat uses 64 bit fields these days.
 #if (VTK_SIZEOF_ID_TYPE == 8) && !defined(_DARWIN_FEATURE_64_BIT_INODE) && !defined(__FreeBSD__)
-  #ifndef WIN32
+  #ifndef _WIN32
     #define USE_STAT_64
   #else
     #define USE_WIN_STAT_64
@@ -64,7 +64,7 @@ namespace
 
 vtkLSDynaFile_t VTK_LSDYNA_OPENFILE(const char* fname)
 {
-#ifndef WIN32
+#ifndef _WIN32
   vtkLSDynaFile_t f = open(fname, O_RDONLY);
   return f;
 #else
diff --git a/IO/LSDyna/private/LSDynaFamily.h b/IO/LSDyna/private/LSDynaFamily.h
index 96c396a9c28..1cd99b90d19 100644
--- a/IO/LSDyna/private/LSDynaFamily.h
+++ b/IO/LSDyna/private/LSDynaFamily.h
@@ -42,7 +42,7 @@
 
 //this is needs to be moved over to fseekpos and ftellpos
 //in the future
-#ifndef WIN32
+#ifndef _WIN32
 #   include <unistd.h>
 typedef off_t vtkLSDynaOff_t; // sanity
 typedef int vtkLSDynaFile_t;
@@ -53,7 +53,7 @@ typedef int vtkLSDynaFile_t;
 #  define VTK_LSDYNA_READ(fid,ptr,cnt) read(fid,ptr,cnt)
 #  define VTK_LSDYNA_ISBADFILE(fid) (fid < 0)
 #  define VTK_LSDYNA_CLOSEFILE(fid) close(fid)
-#else // WIN32
+#else // _WIN32
 typedef long vtkLSDynaOff_t; // insanity
 typedef FILE* vtkLSDynaFile_t;
 #  define VTK_LSDYNA_BADFILE 0
diff --git a/IO/LSDyna/vtkLSDynaReader.cxx b/IO/LSDyna/vtkLSDynaReader.cxx
index cf6104325fe..5067ebac72f 100644
--- a/IO/LSDyna/vtkLSDynaReader.cxx
+++ b/IO/LSDyna/vtkLSDynaReader.cxx
@@ -152,7 +152,7 @@ static const char* vtkLSDynaCellTypes[] =
 
 static void vtkLSGetLine( ifstream& deck, std::string& line )
 {
-#if !defined(_WIN32) && !defined(WIN32) && !defined(_MSC_VER) && !defined(__BORLANDC__)
+#if !defined(_WIN32) && !defined(_MSC_VER) && !defined(__BORLANDC__)
   // One line implementation for everyone but Windows (MSVC6 and BCC32 are the troublemakers):
   std::getline( deck, line, '\n' );
 #else
@@ -3424,11 +3424,11 @@ int vtkLSDynaReader::ReadInputDeckKeywords( ifstream& deck )
       {
       deckExt = "";
       }
-#ifndef WIN32
+#ifndef _WIN32
     xmlSummary = deckDir + "/" + deckName + ".lsdyna";
 #else
     xmlSummary = deckDir + "\\" + deckName + ".lsdyna";
-#endif // WIN32
+#endif // _WIN32
     // As long as we don't kill the input deck, write the summary XML:
     if ( xmlSummary != this->InputDeck )
       {
@@ -3460,11 +3460,11 @@ int vtkLSDynaReader::WriteInputDeckSummary( const char* fname )
   std::string dbName = this->P->Fam.GetDatabaseBaseName();
   if ( this->IsDatabaseValid() && ! dbDir.empty() && ! dbName.empty() )
     {
-#ifndef WIN32
+#ifndef _WIN32
     if ( dbDir[0] == '/' )
 #else
     if ( dbDir[0] == '\\' )
-#endif // WIN32
+#endif // _WIN32
       {
       // OK, we have an absolute path, so it should be safe to write it out.
       xmlSummary
diff --git a/IO/MySQL/vtkMySQLQuery.cxx b/IO/MySQL/vtkMySQLQuery.cxx
index a97b5891dfc..b4e6b62a454 100644
--- a/IO/MySQL/vtkMySQLQuery.cxx
+++ b/IO/MySQL/vtkMySQLQuery.cxx
@@ -25,7 +25,7 @@
 #include <errmsg.h>
 
 
-#if defined(WIN32)
+#if defined(_WIN32)
 # include <string.h>
 # include <locale.h>
 # define LOWERCASE_COMPARE _stricmp
diff --git a/Interaction/Style/vtkInteractorStyleUnicam.cxx b/Interaction/Style/vtkInteractorStyleUnicam.cxx
index 458a0afd2c0..b3617155a68 100644
--- a/Interaction/Style/vtkInteractorStyleUnicam.cxx
+++ b/Interaction/Style/vtkInteractorStyleUnicam.cxx
@@ -39,7 +39,7 @@
 vtkStandardNewMacro(vtkInteractorStyleUnicam);
 
 // define 'TheTime()' function-- returns time in elapsed seconds
-#if defined(_WIN32) || defined(WIN32)
+#if defined(_WIN32)
 # include "vtkWindows.h"
 
 static double TheTime()
diff --git a/Rendering/OpenGL/vtkOpenGLExtensionManager.cxx b/Rendering/OpenGL/vtkOpenGLExtensionManager.cxx
index 302ded28a7a..0d48943f1b3 100644
--- a/Rendering/OpenGL/vtkOpenGLExtensionManager.cxx
+++ b/Rendering/OpenGL/vtkOpenGLExtensionManager.cxx
@@ -870,7 +870,7 @@ void vtkOpenGLExtensionManager::ReadOpenGLExtensions()
     extensions_string += glu_extensions;
     }
 
-#if defined(WIN32)
+#if defined(_WIN32)
   // Don't use this->LoadExtension or we will go into an infinite loop.
   vtkgl::LoadExtension("WGL_ARB_extensions_string", this);
   if (vtkwgl::GetExtensionsStringARB)
diff --git a/Testing/GenericBridge/vtkBridgeExport.h b/Testing/GenericBridge/vtkBridgeExport.h
index 694468f657b..686f36a8b4f 100644
--- a/Testing/GenericBridge/vtkBridgeExport.h
+++ b/Testing/GenericBridge/vtkBridgeExport.h
@@ -26,7 +26,7 @@
 # define VTK_BRIDGE_EXPORT
 #else
 
-#if defined(WIN32) && defined(VTK_BUILD_SHARED_LIBS)
+#if defined(_WIN32) && defined(VTK_BUILD_SHARED_LIBS)
 
  #if defined(vtkBridge_EXPORTS)
   #define VTK_BRIDGE_EXPORT __declspec( dllexport )
diff --git a/ThirdParty/VPIC/VPICGlobal.cxx b/ThirdParty/VPIC/VPICGlobal.cxx
index d57f9c59ca3..a14a9337044 100644
--- a/ThirdParty/VPIC/VPICGlobal.cxx
+++ b/ThirdParty/VPIC/VPICGlobal.cxx
@@ -12,7 +12,7 @@
 #include <iomanip>
 #include <algorithm>
 
-#ifdef WIN32
+#ifdef _WIN32
 const static char * Slash = "\\";
 #else
 const static char * Slash = "/";
diff --git a/ThirdParty/VPIC/VPICView.cxx b/ThirdParty/VPIC/VPICView.cxx
index ef8fc680e81..fc140c52238 100644
--- a/ThirdParty/VPIC/VPICView.cxx
+++ b/ThirdParty/VPIC/VPICView.cxx
@@ -8,7 +8,7 @@
 #include <algorithm>
 #include "math.h"
 
-#ifdef WIN32
+#ifdef _WIN32
 const static char * Slash = "\\";
 #else
 const static char * Slash = "/";
diff --git a/Utilities/DICOMParser/DICOMAppHelper.cxx b/Utilities/DICOMParser/DICOMAppHelper.cxx
index 3e12087c966..d3954b63e68 100644
--- a/Utilities/DICOMParser/DICOMAppHelper.cxx
+++ b/Utilities/DICOMParser/DICOMAppHelper.cxx
@@ -705,7 +705,7 @@ void DICOMAppHelper::TransferSyntaxCallback(DICOMParser *parser,
 {
 
 #ifdef DEBUG_DICOM_APP_HELPER
-#ifdef WIN32
+#ifdef _WIN32
   char platformByteOrder = 'L';
 #else
   char platformByteOrder = 'B';
diff --git a/Utilities/MetaIO/vtkmetaio/localMetaConfiguration.h b/Utilities/MetaIO/vtkmetaio/localMetaConfiguration.h
index 48df5f6ec66..edb39df4348 100644
--- a/Utilities/MetaIO/vtkmetaio/localMetaConfiguration.h
+++ b/Utilities/MetaIO/vtkmetaio/localMetaConfiguration.h
@@ -55,7 +55,7 @@
   #include <iostream>
   #include <fstream>
 
-  #if (defined(_WIN32) || defined(WIN32)) && defined(vtkmetaio_BUILD_SHARED_LIBS)
+  #if defined(_WIN32) && defined(vtkmetaio_BUILD_SHARED_LIBS)
     #ifdef vtkmetaio_EXPORTS
       #define METAIO_EXPORT __declspec(dllexport)
       #define METAIO_EXTERN
diff --git a/Utilities/ParseOGLExt/ParseOGLExt.cxx b/Utilities/ParseOGLExt/ParseOGLExt.cxx
index 3672f26c98d..9654ee3d324 100644
--- a/Utilities/ParseOGLExt/ParseOGLExt.cxx
+++ b/Utilities/ParseOGLExt/ParseOGLExt.cxx
@@ -76,7 +76,7 @@ class Extension {
     switch (itype)
       {
       case WGL:
-        out << "#ifdef WIN32" << endl;
+        out << "#ifdef _WIN32" << endl;
         break;
       case GLX:
        out << "#ifdef VTK_USE_X" << endl;
diff --git a/Wrapping/Java/vtkJavaAwt.h b/Wrapping/Java/vtkJavaAwt.h
index 8f0e83adad0..e78fba8318e 100644
--- a/Wrapping/Java/vtkJavaAwt.h
+++ b/Wrapping/Java/vtkJavaAwt.h
@@ -32,7 +32,7 @@
   #endif
 #endif
 
-#if defined(_WIN32) || defined(WIN32)
+#if defined(_WIN32)
 #define WIN32_JAWT_LOCK_HACK
 #endif
 
@@ -108,7 +108,7 @@ Java_vtk_vtkPanel_RenderCreate(JNIEnv *env, jobject canvas, jobject id0)
     }
 
 // Here is the win32 drawing code
-#if defined(_WIN32) || defined(WIN32)
+#if defined(_WIN32)
   temp0->Finalize();
   JAWT_Win32DrawingSurfaceInfo* dsi_win;
   dsi_win = (JAWT_Win32DrawingSurfaceInfo*)dsi->platformInfo;
@@ -209,7 +209,7 @@ Java_vtk_rendering_awt_vtkInternalAwtComponent_RenderCreate(JNIEnv *env, jobject
     }
 
 // Here is the win32 drawing code
-#if defined(_WIN32) || defined(WIN32)
+#if defined(_WIN32)
   temp0->Finalize();
   JAWT_Win32DrawingSurfaceInfo* dsi_win;
   dsi_win = (JAWT_Win32DrawingSurfaceInfo*)dsi->platformInfo;
diff --git a/Wrapping/Tcl/vtkTclUtil.h b/Wrapping/Tcl/vtkTclUtil.h
index e196067367c..45db3c0b4a0 100644
--- a/Wrapping/Tcl/vtkTclUtil.h
+++ b/Wrapping/Tcl/vtkTclUtil.h
@@ -20,7 +20,7 @@
 #include "vtkCommand.h"
 #include "vtkTcl.h"
 
-#ifdef WIN32
+#ifdef _WIN32
 #define VTKTCL_EXPORT __declspec( dllexport )
 #else
 #define VTKTCL_EXPORT