diff --git a/Help/policy/CMP0021.rst b/Help/policy/CMP0021.rst
index 2c49c33cb1..b9074ab156 100644
--- a/Help/policy/CMP0021.rst
+++ b/Help/policy/CMP0021.rst
@@ -1,6 +1,9 @@
 CMP0021
 -------
 
+.. |REMOVED_IN_CMAKE_VERSION| replace:: 4.0
+.. include:: REMOVED_PROLOGUE.txt
+
 Fatal error on relative paths in :prop_tgt:`INCLUDE_DIRECTORIES` target
 property.
 
@@ -15,7 +18,5 @@ policy is to issue a ``FATAL_ERROR`` if ``INCLUDE_DIRECTORIES`` contains a
 relative path.
 
 .. |INTRODUCED_IN_CMAKE_VERSION| replace:: 2.8.12
-.. |WARNS_OR_DOES_NOT_WARN| replace:: warns
-.. include:: STANDARD_ADVICE.txt
-
-.. include:: DEPRECATED.txt
+.. |WARNED_OR_DID_NOT_WARN| replace:: warned
+.. include:: REMOVED_EPILOGUE.txt
diff --git a/Source/cmGeneratorTarget_IncludeDirectories.cxx b/Source/cmGeneratorTarget_IncludeDirectories.cxx
index fc89331bef..cc6ec0cecd 100644
--- a/Source/cmGeneratorTarget_IncludeDirectories.cxx
+++ b/Source/cmGeneratorTarget_IncludeDirectories.cxx
@@ -185,7 +185,6 @@ void processIncludeDirectories(cmGeneratorTarget const* tgt,
 
       if (!cmSystemTools::FileIsFullPath(entryInclude)) {
         std::ostringstream e;
-        bool noMessage = false;
         MessageType messageType = MessageType::FATAL_ERROR;
         if (!targetName.empty()) {
           /* clang-format off */
@@ -194,27 +193,13 @@ void processIncludeDirectories(cmGeneratorTarget const* tgt,
             "  \"" << entryInclude << "\"";
           /* clang-format on */
         } else {
-          switch (tgt->GetPolicyStatusCMP0021()) {
-            case cmPolicies::WARN: {
-              e << cmPolicies::GetPolicyWarning(cmPolicies::CMP0021) << "\n";
-              messageType = MessageType::AUTHOR_WARNING;
-            } break;
-            case cmPolicies::OLD:
-              noMessage = true;
-              break;
-            case cmPolicies::NEW:
-              // Issue the fatal message.
-              break;
-          }
           e << "Found relative path while evaluating include directories of "
                "\""
             << tgt->GetName() << "\":\n  \"" << entryInclude << "\"\n";
         }
-        if (!noMessage) {
-          tgt->GetLocalGenerator()->IssueMessage(messageType, e.str());
-          if (messageType == MessageType::FATAL_ERROR) {
-            return;
-          }
+        tgt->GetLocalGenerator()->IssueMessage(messageType, e.str());
+        if (messageType == MessageType::FATAL_ERROR) {
+          return;
         }
       }
 
diff --git a/Source/cmPolicies.h b/Source/cmPolicies.h
index 55c977e301..51e9333576 100644
--- a/Source/cmPolicies.h
+++ b/Source/cmPolicies.h
@@ -76,7 +76,7 @@ class cmMakefile;
   SELECT(                                                                     \
     POLICY, CMP0021,                                                          \
     "Fatal error on relative paths in INCLUDE_DIRECTORIES target property.",  \
-    2, 8, 12, WARN)                                                           \
+    2, 8, 12, NEW)                                                            \
   SELECT(POLICY, CMP0022,                                                     \
          "INTERFACE_LINK_LIBRARIES defines the link interface.", 2, 8, 12,    \
          WARN)                                                                \
diff --git a/Tests/IncludeDirectories/CMP0021/CMakeLists.txt b/Tests/IncludeDirectories/CMP0021/CMakeLists.txt
deleted file mode 100644
index 0b9aee899a..0000000000
--- a/Tests/IncludeDirectories/CMP0021/CMakeLists.txt
+++ /dev/null
@@ -1,14 +0,0 @@
-
-cmake_policy(SET CMP0021 OLD)
-add_executable(cmp0021exe main.cpp)
-
-if(NOT CMAKE_CURRENT_BINARY_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
-  file(MAKE_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/includes")
-  execute_process(COMMAND ${CMAKE_COMMAND} -E
-    copy_directory
-    "${CMAKE_CURRENT_SOURCE_DIR}/includes"
-    "${CMAKE_CURRENT_BINARY_DIR}/includes"
-  )
-endif()
-set_property(TARGET cmp0021exe PROPERTY
-  INCLUDE_DIRECTORIES includes/cmp0021)
diff --git a/Tests/IncludeDirectories/CMP0021/includes/cmp0021/cmp0021.h b/Tests/IncludeDirectories/CMP0021/includes/cmp0021/cmp0021.h
deleted file mode 100644
index 3d49b31d57..0000000000
--- a/Tests/IncludeDirectories/CMP0021/includes/cmp0021/cmp0021.h
+++ /dev/null
@@ -1,2 +0,0 @@
-
-#define CMP0021_DEFINE
diff --git a/Tests/IncludeDirectories/CMP0021/main.cpp b/Tests/IncludeDirectories/CMP0021/main.cpp
deleted file mode 100644
index 0f87dd9970..0000000000
--- a/Tests/IncludeDirectories/CMP0021/main.cpp
+++ /dev/null
@@ -1,11 +0,0 @@
-
-#include "cmp0021.h"
-
-#ifndef CMP0021_DEFINE
-#  error Expected CMP0021_DEFINE
-#endif
-
-int main(int, char**)
-{
-  return 0;
-}
diff --git a/Tests/IncludeDirectories/CMakeLists.txt b/Tests/IncludeDirectories/CMakeLists.txt
index e9c1c63637..854a42a103 100644
--- a/Tests/IncludeDirectories/CMakeLists.txt
+++ b/Tests/IncludeDirectories/CMakeLists.txt
@@ -206,7 +206,3 @@ get_target_property(incs empty_entry_test INCLUDE_DIRECTORIES)
 if (NOT incs STREQUAL ";/one/two")
   message(SEND_ERROR "Empty include_directories entry was not ignored.")
 endif()
-
-if(NOT CMAKE_GENERATOR STREQUAL "Xcode" AND NOT CMAKE_GENERATOR MATCHES "Ninja")
-  add_subdirectory(CMP0021)
-endif()
diff --git a/Tests/RunCMake/include_directories/CMP0021.cmake b/Tests/RunCMake/include_directories/CMP0021.cmake
index f18666b076..63b1930e17 100644
--- a/Tests/RunCMake/include_directories/CMP0021.cmake
+++ b/Tests/RunCMake/include_directories/CMP0021.cmake
@@ -1,7 +1,5 @@
 enable_language(CXX)
 
-cmake_policy(SET CMP0021 NEW)
-
 add_library(testTarget "${CMAKE_CURRENT_SOURCE_DIR}/empty.cpp")
 set_property(TARGET testTarget PROPERTY INTERFACE_INCLUDE_DIRECTORIES "$<1:foo>")