diff --git a/Help/manual/cmake-variables.7.rst b/Help/manual/cmake-variables.7.rst
index b367ffcd57..200fc18e86 100644
--- a/Help/manual/cmake-variables.7.rst
+++ b/Help/manual/cmake-variables.7.rst
@@ -323,6 +323,7 @@ Variables that Describe the System
 .. toctree::
    :maxdepth: 1
 
+   /variable/AIX
    /variable/ANDROID
    /variable/APPLE
    /variable/BORLAND
@@ -331,6 +332,7 @@ Variables that Describe the System
    /variable/CMAKE_CL_64
    /variable/CMAKE_COMPILER_2005
    /variable/CMAKE_HOST_APPLE
+   /variable/CMAKE_HOST_AIX
    /variable/CMAKE_HOST_BSD
    /variable/CMAKE_HOST_EXECUTABLE_SUFFIX
    /variable/CMAKE_HOST_LINUX
diff --git a/Help/release/4.0.rst b/Help/release/4.0.rst
index a00d3b7236..9e48ec7dd2 100644
--- a/Help/release/4.0.rst
+++ b/Help/release/4.0.rst
@@ -41,6 +41,9 @@ Commands
 Variables
 ---------
 
+* The :variable:`AIX` and :variable:`CMAKE_HOST_AIX` variables are
+  now set to true when the target or host system is AIX, respectively.
+
 * Linker flag variables learned to support the ``LINKER:`` prefix:
 
   * :variable:`CMAKE_EXE_LINKER_FLAGS`
diff --git a/Help/variable/AIX.rst b/Help/variable/AIX.rst
new file mode 100644
index 0000000000..b07418df12
--- /dev/null
+++ b/Help/variable/AIX.rst
@@ -0,0 +1,6 @@
+AIX
+---
+
+.. versionadded:: 4.0
+
+Set to true when the target system is AIX.
diff --git a/Help/variable/CMAKE_HOST_AIX.rst b/Help/variable/CMAKE_HOST_AIX.rst
new file mode 100644
index 0000000000..8037796da4
--- /dev/null
+++ b/Help/variable/CMAKE_HOST_AIX.rst
@@ -0,0 +1,6 @@
+CMAKE_HOST_AIX
+--------------
+
+.. versionadded:: 4.0
+
+Set to true when the host system is AIX.
diff --git a/Modules/CMakeSystemSpecificInitialize.cmake b/Modules/CMakeSystemSpecificInitialize.cmake
index ee8cb860c2..313187795a 100644
--- a/Modules/CMakeSystemSpecificInitialize.cmake
+++ b/Modules/CMakeSystemSpecificInitialize.cmake
@@ -17,6 +17,7 @@ unset(MSYS)
 unset(WIN32)
 unset(BSD)
 unset(LINUX)
+unset(AIX)
 
 # The CMAKE_EFFECTIVE_SYSTEM_NAME is used to load compiler and compiler
 # wrapper configuration files. By default it equals to CMAKE_SYSTEM_NAME
diff --git a/Modules/Platform/AIX-Initialize.cmake b/Modules/Platform/AIX-Initialize.cmake
index 0b117a7b2f..b42e58e06d 100644
--- a/Modules/Platform/AIX-Initialize.cmake
+++ b/Modules/Platform/AIX-Initialize.cmake
@@ -1 +1,2 @@
+set(AIX 1)
 set(UNIX 1)
diff --git a/Source/cmStateSnapshot.cxx b/Source/cmStateSnapshot.cxx
index 8de9188779..ec84323488 100644
--- a/Source/cmStateSnapshot.cxx
+++ b/Source/cmStateSnapshot.cxx
@@ -325,6 +325,11 @@ void cmStateSnapshot::SetDefaultDefinitions()
   this->SetDefinition("CMAKE_HOST_LINUX", "1");
 #endif
 
+#if defined(_AIX)
+  this->SetDefinition("AIX", "1");
+  this->SetDefinition("CMAKE_HOST_AIX", "1");
+#endif
+
   this->SetDefinition("CMAKE_MAJOR_VERSION",
                       std::to_string(cmVersion::GetMajorVersion()));
   this->SetDefinition("CMAKE_MINOR_VERSION",