diff --git a/History.md b/History.md
--- a/History.md
+++ b/History.md
@@ -11,6 +11,10 @@
 ===
 ## R02-0X-00
 
+
+23 Apr 2024 Thomas Latham
+* Drop redundant EVTGEN\_CPP11 preprocessor switch
+
 22 Apr 2024 Fernando Abudinen
 * D116: Replaced PHOTOS with FSR flags in examples and tests.
 
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -35,7 +35,6 @@
 # build both the shared and static libs
 add_library(objlib OBJECT ${EVTGEN_SOURCES})
 set_target_properties(objlib PROPERTIES POSITION_INDEPENDENT_CODE 1)
-target_compile_definitions(objlib PRIVATE EVTGEN_CPP11)
 target_include_directories(objlib PRIVATE ${CMAKE_SOURCE_DIR})
 if(EVTGEN_HEPMC3)
     target_compile_definitions(objlib PRIVATE EVTGEN_HEPMC3)
@@ -57,7 +56,6 @@
 set_target_properties(EvtGen PROPERTIES OUTPUT_NAME EvtGen)
 set_target_properties(EvtGen PROPERTIES VERSION ${PROJECT_VERSION} SOVERSION ${PROJECT_VERSION_MAJOR} )
 set_target_properties(EvtGen PROPERTIES LIBRARY_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/${CMAKE_INSTALL_LIBDIR})
-target_compile_definitions(EvtGen PUBLIC EVTGEN_CPP11)
 target_include_directories(EvtGen PUBLIC $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}> $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
 if(EVTGEN_HEPMC3)
     target_compile_definitions(EvtGen PUBLIC EVTGEN_HEPMC3)
@@ -72,7 +70,6 @@
 add_library(EvtGenStatic STATIC $<TARGET_OBJECTS:objlib>)
 set_target_properties(EvtGenStatic PROPERTIES OUTPUT_NAME EvtGen)
 set_target_properties(EvtGenStatic PROPERTIES ARCHIVE_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/${CMAKE_INSTALL_LIBDIR})
-target_compile_definitions(EvtGenStatic PUBLIC EVTGEN_CPP11)
 target_include_directories(EvtGenStatic PUBLIC $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}> $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
 if(EVTGEN_HEPMC3)
     target_compile_definitions(EvtGenStatic PUBLIC EVTGEN_HEPMC3)
@@ -91,7 +88,6 @@
     # used to build both the shared and static libs
     add_library(objlib_ext OBJECT ${EVTGEN_EXTERNAL_SOURCES})
     set_target_properties(objlib_ext PROPERTIES POSITION_INDEPENDENT_CODE 1)
-    target_compile_definitions(objlib_ext PRIVATE EVTGEN_CPP11)
     target_include_directories(objlib_ext PRIVATE ${CMAKE_SOURCE_DIR})
     if(EVTGEN_HEPMC3)
         target_compile_definitions(objlib_ext PRIVATE EVTGEN_HEPMC3)
@@ -140,7 +136,6 @@
     set_target_properties(EvtGenExternal PROPERTIES OUTPUT_NAME EvtGenExternal)
     set_target_properties(EvtGenExternal PROPERTIES VERSION ${PROJECT_VERSION} SOVERSION ${PROJECT_VERSION_MAJOR} )
     set_target_properties(EvtGenExternal PROPERTIES LIBRARY_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/${CMAKE_INSTALL_LIBDIR})
-    target_compile_definitions(EvtGenExternal PUBLIC EVTGEN_CPP11)
     target_include_directories(EvtGenExternal PUBLIC $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}> $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
     if(EVTGEN_PYTHIA)
         target_compile_definitions(EvtGenExternal PUBLIC EVTGEN_PYTHIA)
@@ -198,7 +193,6 @@
     add_library(EvtGenExternalStatic STATIC $<TARGET_OBJECTS:objlib_ext>)
     set_target_properties(EvtGenExternalStatic PROPERTIES OUTPUT_NAME EvtGenExternal)
     set_target_properties(EvtGenExternalStatic PROPERTIES ARCHIVE_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/${CMAKE_INSTALL_LIBDIR})
-    target_compile_definitions(EvtGenExternalStatic PUBLIC EVTGEN_CPP11)
     target_include_directories(EvtGenExternalStatic PUBLIC $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}> $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
     if(EVTGEN_PYTHIA)
         target_compile_definitions(EvtGenExternalStatic PUBLIC EVTGEN_PYTHIA)
diff --git a/test/evt_dalitz.cc b/test/evt_dalitz.cc
--- a/test/evt_dalitz.cc
+++ b/test/evt_dalitz.cc
@@ -89,14 +89,8 @@
     // Initialize EvtGen
 
     // Define the random number generator
-    EvtRandomEngine* eng = nullptr;
-
-#ifdef EVTGEN_CPP11
-    // Use the Mersenne-Twister generator (C++11 only)
-    eng = new EvtMTRandomEngine();
-#else
-    eng = new EvtSimpleRandomEngine();
-#endif
+    // Use the Mersenne-Twister generator
+    EvtRandomEngine* eng = new EvtMTRandomEngine();
 
     EvtRandom::setRandomEngine( eng );
 
diff --git a/test/evtgenlhc_test1.cc b/test/evtgenlhc_test1.cc
--- a/test/evtgenlhc_test1.cc
+++ b/test/evtgenlhc_test1.cc
@@ -161,14 +161,8 @@
 int main( int argc, char* argv[] )
 {
     // Define the random number generator
-    EvtRandomEngine* myRandomEngine = nullptr;
-
-#ifdef EVTGEN_CPP11
-    // Use the Mersenne-Twister generator (C++11 only)
-    myRandomEngine = new EvtMTRandomEngine();
-#else
-    myRandomEngine = new EvtSimpleRandomEngine();
-#endif
+    // Use the Mersenne-Twister generator
+    EvtRandomEngine* myRandomEngine = new EvtMTRandomEngine();
 
     if ( !TROOT::Initialized() ) {
         static TROOT root( "RooTuple", "RooTuple ROOT in EvtGen" );
diff --git a/test/example1.cc b/test/example1.cc
--- a/test/example1.cc
+++ b/test/example1.cc
@@ -49,14 +49,8 @@
     EvtParticle* parent( nullptr );
 
     // Define the random number generator
-    EvtRandomEngine* eng = nullptr;
-
-#ifdef EVTGEN_CPP11
-    // Use the Mersenne-Twister generator (C++11 only)
-    eng = new EvtMTRandomEngine();
-#else
-    eng = new EvtSimpleRandomEngine();
-#endif
+    // Use the Mersenne-Twister generator
+    EvtRandomEngine* eng = new EvtMTRandomEngine();
 
     EvtRandom::setRandomEngine( eng );
 
diff --git a/test/exampleWriteHepMC.cc b/test/exampleWriteHepMC.cc
--- a/test/exampleWriteHepMC.cc
+++ b/test/exampleWriteHepMC.cc
@@ -88,14 +88,8 @@
     EvtParticle* parent( nullptr );
 
     // Define the random number generator
-    EvtRandomEngine* eng = nullptr;
-
-#ifdef EVTGEN_CPP11
-    // Use the Mersenne-Twister generator (C++11 only)
-    eng = new EvtMTRandomEngine();
-#else
-    eng = new EvtSimpleRandomEngine();
-#endif
+    // Use the Mersenne-Twister generator
+    EvtRandomEngine* eng = new EvtMTRandomEngine();
 
     EvtRandom::setRandomEngine( eng );
 
diff --git a/validation/genExampleRootFiles.cc b/validation/genExampleRootFiles.cc
--- a/validation/genExampleRootFiles.cc
+++ b/validation/genExampleRootFiles.cc
@@ -132,14 +132,8 @@
     EvtParticle* theParent( nullptr );
 
     // Define the random number generator
-    EvtRandomEngine* myRandomEngine = nullptr;
-
-#ifdef EVTGEN_CPP11
-    // Use the Mersenne-Twister generator (C++11 only)
-    myRandomEngine = new EvtMTRandomEngine();
-#else
-    myRandomEngine = new EvtSimpleRandomEngine();
-#endif
+    // Use the Mersenne-Twister generator
+    EvtRandomEngine* myRandomEngine = new EvtMTRandomEngine();
 
     // Initialize the generator - read in the decay table and particle properties.
     // For our validation purposes, we just want to read in one decay file and create
diff --git a/validation/genRootDecayChain.cc b/validation/genRootDecayChain.cc
--- a/validation/genRootDecayChain.cc
+++ b/validation/genRootDecayChain.cc
@@ -178,17 +178,12 @@
 
 void genRootDecayChain::generateEvents()
 {
-    EvtRandomEngine* randomEngine = nullptr;
     EvtAbsRadCorr* radCorrEngine = nullptr;
     std::list<EvtDecayBase*> extraModels;
 
     // Define the random number generator
-#ifdef EVTGEN_CPP11
-    // Use the Mersenne-Twister generator (C++11 only)
-    randomEngine = new EvtMTRandomEngine();
-#else
-    randomEngine = new EvtSimpleRandomEngine();
-#endif
+    // Use the Mersenne-Twister generator
+    EvtRandomEngine* randomEngine = new EvtMTRandomEngine();
 
     // Initialize the generator - read in the decay table and particle properties.
     // For our validation purposes, we just want to read in one decay file
diff --git a/validation/testCPVDecays.cc b/validation/testCPVDecays.cc
--- a/validation/testCPVDecays.cc
+++ b/validation/testCPVDecays.cc
@@ -110,15 +110,8 @@
          << " (used to draw oscillation maxima lines)" << endl;
 
     // Define the random number generator
-
-    EvtRandomEngine* myRandomEngine = nullptr;
-
-#ifdef EVTGEN_CPP11
-    // Use the Mersenne-Twister generator (C++11 only)
-    myRandomEngine = new EvtMTRandomEngine();
-#else
-    myRandomEngine = new EvtSimpleRandomEngine();
-#endif
+    // Use the Mersenne-Twister generator
+    EvtRandomEngine* myRandomEngine = new EvtMTRandomEngine();
 
     EvtAbsRadCorr* radCorrEngine = nullptr;
     std::list<EvtDecayBase*> extraModels;