diff --git a/Help/release/dev/deprecate-policy-old.rst b/Help/release/dev/deprecate-policy-old.rst
new file mode 100644
index 0000000000..9ae30e67a6
--- /dev/null
+++ b/Help/release/dev/deprecate-policy-old.rst
@@ -0,0 +1,7 @@
+deprecate-policy-old
+--------------------
+
+* An explicit deprecation diagnostic was added for policies ``CMP0036``
+  and below.  The :manual:`cmake-policies(7)` manual explains that the
+  OLD behaviors of all policies are deprecated and that projects should
+  port to the NEW behaviors.
diff --git a/Source/cmMakefile.cxx b/Source/cmMakefile.cxx
index 4ed76c7b16..b8a5293ac4 100644
--- a/Source/cmMakefile.cxx
+++ b/Source/cmMakefile.cxx
@@ -4002,6 +4002,13 @@ bool cmMakefile::SetPolicy(cmPolicies::PolicyID id,
     return false;
   }
 
+  // Deprecate old policies, especially those that require a lot
+  // of code to maintain the old behavior.
+  if (status == cmPolicies::OLD && id <= cmPolicies::CMP0036) {
+    this->IssueMessage(cmake::DEPRECATION_WARNING,
+                       cmPolicies::GetPolicyDeprecatedWarning(id));
+  }
+
   this->StateSnapshot.SetPolicy(id, status);
   return true;
 }
diff --git a/Source/cmPolicies.cxx b/Source/cmPolicies.cxx
index 837557b7f8..da3edd427e 100644
--- a/Source/cmPolicies.cxx
+++ b/Source/cmPolicies.cxx
@@ -275,6 +275,22 @@ std::string cmPolicies::GetPolicyWarning(cmPolicies::PolicyID id)
   return msg.str();
 }
 
+std::string cmPolicies::GetPolicyDeprecatedWarning(cmPolicies::PolicyID id)
+{
+  std::ostringstream msg;
+  /* clang-format off */
+  msg <<
+    "The OLD behavior for policy " << idToString(id) << " "
+    "will be removed from a future version of CMake.\n"
+    "The cmake-policies(7) manual explains that the OLD behaviors of all "
+    "policies are deprecated and that a policy should be set to OLD only "
+    "under specific short-term circumstances.  Projects should be ported "
+    "to the NEW behavior and not rely on setting a policy to OLD."
+    ;
+  /* clang-format on */
+  return msg.str();
+}
+
 ///! return an error string for when a required policy is unspecified
 std::string cmPolicies::GetRequiredPolicyError(cmPolicies::PolicyID id)
 {
diff --git a/Source/cmPolicies.h b/Source/cmPolicies.h
index 120beb6820..69cbc1844e 100644
--- a/Source/cmPolicies.h
+++ b/Source/cmPolicies.h
@@ -279,6 +279,7 @@ public:
 
   ///! return a warning string for a given policy
   static std::string GetPolicyWarning(cmPolicies::PolicyID id);
+  static std::string GetPolicyDeprecatedWarning(cmPolicies::PolicyID id);
 
   ///! return an error string for when a required policy is unspecified
   static std::string GetRequiredPolicyError(cmPolicies::PolicyID id);
diff --git a/Tests/RunCMake/CMP0019/CMP0019-OLD-stderr.txt b/Tests/RunCMake/CMP0019/CMP0019-OLD-stderr.txt
new file mode 100644
index 0000000000..048762d000
--- /dev/null
+++ b/Tests/RunCMake/CMP0019/CMP0019-OLD-stderr.txt
@@ -0,0 +1,10 @@
+^CMake Deprecation Warning at CMP0019-OLD.cmake:[0-9]+ \(cmake_policy\):
+  The OLD behavior for policy CMP0019 will be removed from a future version
+  of CMake.
+
+  The cmake-policies\(7\) manual explains that the OLD behaviors of all
+  policies are deprecated and that a policy should be set to OLD only under
+  specific short-term circumstances.  Projects should be ported to the NEW
+  behavior and not rely on setting a policy to OLD.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:[0-9]+ \(include\)$
diff --git a/Tests/RunCMake/CMP0026/CMP0026-CONFIG-LOCATION-OLD-stderr.txt b/Tests/RunCMake/CMP0026/CMP0026-CONFIG-LOCATION-OLD-stderr.txt
new file mode 100644
index 0000000000..edeb337280
--- /dev/null
+++ b/Tests/RunCMake/CMP0026/CMP0026-CONFIG-LOCATION-OLD-stderr.txt
@@ -0,0 +1,10 @@
+^CMake Deprecation Warning at CMP0026-CONFIG-LOCATION-OLD.cmake:[0-9]+ \(cmake_policy\):
+  The OLD behavior for policy CMP0026 will be removed from a future version
+  of CMake.
+
+  The cmake-policies\(7\) manual explains that the OLD behaviors of all
+  policies are deprecated and that a policy should be set to OLD only under
+  specific short-term circumstances.  Projects should be ported to the NEW
+  behavior and not rely on setting a policy to OLD.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:[0-9]+ \(include\)$
diff --git a/Tests/RunCMake/CMP0026/CMP0026-LOCATION-CONFIG-OLD-stderr.txt b/Tests/RunCMake/CMP0026/CMP0026-LOCATION-CONFIG-OLD-stderr.txt
new file mode 100644
index 0000000000..32ff698f1c
--- /dev/null
+++ b/Tests/RunCMake/CMP0026/CMP0026-LOCATION-CONFIG-OLD-stderr.txt
@@ -0,0 +1,10 @@
+^CMake Deprecation Warning at CMP0026-LOCATION-CONFIG-OLD.cmake:[0-9]+ \(cmake_policy\):
+  The OLD behavior for policy CMP0026 will be removed from a future version
+  of CMake.
+
+  The cmake-policies\(7\) manual explains that the OLD behaviors of all
+  policies are deprecated and that a policy should be set to OLD only under
+  specific short-term circumstances.  Projects should be ported to the NEW
+  behavior and not rely on setting a policy to OLD.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:[0-9]+ \(include\)$
diff --git a/Tests/RunCMake/CMP0026/CMP0026-OLD-stderr.txt b/Tests/RunCMake/CMP0026/CMP0026-OLD-stderr.txt
new file mode 100644
index 0000000000..b3f79fc4da
--- /dev/null
+++ b/Tests/RunCMake/CMP0026/CMP0026-OLD-stderr.txt
@@ -0,0 +1,10 @@
+^CMake Deprecation Warning at CMP0026-OLD.cmake:[0-9]+ \(cmake_policy\):
+  The OLD behavior for policy CMP0026 will be removed from a future version
+  of CMake.
+
+  The cmake-policies\(7\) manual explains that the OLD behaviors of all
+  policies are deprecated and that a policy should be set to OLD only under
+  specific short-term circumstances.  Projects should be ported to the NEW
+  behavior and not rely on setting a policy to OLD.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:[0-9]+ \(include\)$
diff --git a/Tests/RunCMake/CMP0026/clear-cached-information-stderr.txt b/Tests/RunCMake/CMP0026/clear-cached-information-stderr.txt
new file mode 100644
index 0000000000..157a0468a9
--- /dev/null
+++ b/Tests/RunCMake/CMP0026/clear-cached-information-stderr.txt
@@ -0,0 +1,10 @@
+^CMake Deprecation Warning at clear-cached-information.cmake:[0-9]+ \(cmake_policy\):
+  The OLD behavior for policy CMP0026 will be removed from a future version
+  of CMake.
+
+  The cmake-policies\(7\) manual explains that the OLD behaviors of all
+  policies are deprecated and that a policy should be set to OLD only under
+  specific short-term circumstances.  Projects should be ported to the NEW
+  behavior and not rely on setting a policy to OLD.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:[0-9]+ \(include\)$
diff --git a/Tests/RunCMake/CMP0028/CMP0028-OLD-iface-stderr.txt b/Tests/RunCMake/CMP0028/CMP0028-OLD-iface-stderr.txt
new file mode 100644
index 0000000000..b7a07559ff
--- /dev/null
+++ b/Tests/RunCMake/CMP0028/CMP0028-OLD-iface-stderr.txt
@@ -0,0 +1,10 @@
+^CMake Deprecation Warning at CMP0028-OLD-iface.cmake:[0-9]+ \(cmake_policy\):
+  The OLD behavior for policy CMP0028 will be removed from a future version
+  of CMake.
+
+  The cmake-policies\(7\) manual explains that the OLD behaviors of all
+  policies are deprecated and that a policy should be set to OLD only under
+  specific short-term circumstances.  Projects should be ported to the NEW
+  behavior and not rely on setting a policy to OLD.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:[0-9]+ \(include\)$
diff --git a/Tests/RunCMake/CMP0028/CMP0028-OLD-stderr.txt b/Tests/RunCMake/CMP0028/CMP0028-OLD-stderr.txt
new file mode 100644
index 0000000000..586a876a0a
--- /dev/null
+++ b/Tests/RunCMake/CMP0028/CMP0028-OLD-stderr.txt
@@ -0,0 +1,10 @@
+^CMake Deprecation Warning at CMP0028-OLD.cmake:[0-9]+ \(cmake_policy\):
+  The OLD behavior for policy CMP0028 will be removed from a future version
+  of CMake.
+
+  The cmake-policies\(7\) manual explains that the OLD behaviors of all
+  policies are deprecated and that a policy should be set to OLD only under
+  specific short-term circumstances.  Projects should be ported to the NEW
+  behavior and not rely on setting a policy to OLD.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:[0-9]+ \(include\)$
diff --git a/Tests/RunCMake/DisallowedCommands/CMP0029-OLD-stderr.txt b/Tests/RunCMake/DisallowedCommands/CMP0029-OLD-stderr.txt
new file mode 100644
index 0000000000..430c86527a
--- /dev/null
+++ b/Tests/RunCMake/DisallowedCommands/CMP0029-OLD-stderr.txt
@@ -0,0 +1,10 @@
+^CMake Deprecation Warning at CMP0029-OLD.cmake:[0-9]+ \(cmake_policy\):
+  The OLD behavior for policy CMP0029 will be removed from a future version
+  of CMake.
+
+  The cmake-policies\(7\) manual explains that the OLD behaviors of all
+  policies are deprecated and that a policy should be set to OLD only under
+  specific short-term circumstances.  Projects should be ported to the NEW
+  behavior and not rely on setting a policy to OLD.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:[0-9]+ \(include\)$
diff --git a/Tests/RunCMake/DisallowedCommands/CMP0030-OLD-stderr.txt b/Tests/RunCMake/DisallowedCommands/CMP0030-OLD-stderr.txt
index e95e16f869..d00b8272ba 100644
--- a/Tests/RunCMake/DisallowedCommands/CMP0030-OLD-stderr.txt
+++ b/Tests/RunCMake/DisallowedCommands/CMP0030-OLD-stderr.txt
@@ -1,4 +1,15 @@
-^CMake Error at CMP0030-OLD.cmake:2 \(use_mangled_mesa\):
+^CMake Deprecation Warning at CMP0030-OLD.cmake:[0-9]+ \(cmake_policy\):
+  The OLD behavior for policy CMP0030 will be removed from a future version
+  of CMake.
+
+  The cmake-policies\(7\) manual explains that the OLD behaviors of all
+  policies are deprecated and that a policy should be set to OLD only under
+  specific short-term circumstances.  Projects should be ported to the NEW
+  behavior and not rely on setting a policy to OLD.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:[0-9]+ \(include\)
++
+CMake Error at CMP0030-OLD.cmake:2 \(use_mangled_mesa\):
   use_mangled_mesa called with incorrect number of arguments
 Call Stack \(most recent call first\):
   CMakeLists.txt:3 \(include\)$
diff --git a/Tests/RunCMake/TargetSources/CMP0026-LOCATION-stderr.txt b/Tests/RunCMake/TargetSources/CMP0026-LOCATION-stderr.txt
new file mode 100644
index 0000000000..d7ccedb1b4
--- /dev/null
+++ b/Tests/RunCMake/TargetSources/CMP0026-LOCATION-stderr.txt
@@ -0,0 +1,10 @@
+^CMake Deprecation Warning at CMP0026-LOCATION.cmake:[0-9]+ \(cmake_policy\):
+  The OLD behavior for policy CMP0026 will be removed from a future version
+  of CMake.
+
+  The cmake-policies\(7\) manual explains that the OLD behaviors of all
+  policies are deprecated and that a policy should be set to OLD only under
+  specific short-term circumstances.  Projects should be ported to the NEW
+  behavior and not rely on setting a policy to OLD.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:[0-9]+ \(include\)$