diff --git a/Help/command/string.rst b/Help/command/string.rst
index 34c1b6179..bc4399c05 100644
--- a/Help/command/string.rst
+++ b/Help/command/string.rst
@@ -15,6 +15,7 @@ String operations.
   string(REPLACE <match_string>
          <replace_string> <output variable>
          <input> [<input>...])
+  string(APPEND <string variable> [<input>...])
   string(CONCAT <output variable> [<input>...])
   string(<MD5|SHA1|SHA224|SHA256|SHA384|SHA512>
          <output variable> <input>)
@@ -55,6 +56,8 @@ through argument parsing.
 ``REPLACE`` will replace all occurrences of ``match_string`` in the input
 with ``replace_string`` and store the result in the output.
 
+``APPEND`` will append all the input arguments to the string.
+
 ``CONCAT`` will concatenate all the input arguments together and store
 the result in the named output variable.
 
diff --git a/Help/release/dev/string-append.rst b/Help/release/dev/string-append.rst
new file mode 100644
index 000000000..190b51ee7
--- /dev/null
+++ b/Help/release/dev/string-append.rst
@@ -0,0 +1,4 @@
+string-append
+-------------
+
+* The :command:`string` command learned a new ``APPEND`` subcommand.
diff --git a/Source/cmStringCommand.cxx b/Source/cmStringCommand.cxx
index edc6afc19..efc1f1627 100644
--- a/Source/cmStringCommand.cxx
+++ b/Source/cmStringCommand.cxx
@@ -74,6 +74,10 @@ bool cmStringCommand
     {
     return this->HandleLengthCommand(args);
     }
+  else if(subCommand == "APPEND")
+    {
+    return this->HandleAppendCommand(args);
+    }
   else if(subCommand == "CONCAT")
     {
     return this->HandleConcatCommand(args);
@@ -729,6 +733,34 @@ bool cmStringCommand
   return true;
 }
 
+//----------------------------------------------------------------------------
+bool cmStringCommand::HandleAppendCommand(std::vector<std::string> const& args)
+{
+  if(args.size() < 2)
+    {
+    this->SetError("sub-command APPEND requires at least one argument.");
+    return false;
+    }
+
+  // Skip if nothing to append.
+  if(args.size() < 3)
+    {
+    return true;
+    }
+
+  const std::string& variable = args[1];
+
+  std::string value;
+  const char* oldValue = this->Makefile->GetDefinition(variable);
+  if(oldValue)
+    {
+    value = oldValue;
+    }
+  value += cmJoin(cmRange(args).advance(2), std::string());
+  this->Makefile->AddDefinition(variable, value.c_str());
+  return true;
+}
+
 //----------------------------------------------------------------------------
 bool cmStringCommand
 ::HandleConcatCommand(std::vector<std::string> const& args)
diff --git a/Source/cmStringCommand.h b/Source/cmStringCommand.h
index 9c75095c1..3ed17ebd3 100644
--- a/Source/cmStringCommand.h
+++ b/Source/cmStringCommand.h
@@ -67,6 +67,7 @@ protected:
   bool HandleReplaceCommand(std::vector<std::string> const& args);
   bool HandleLengthCommand(std::vector<std::string> const& args);
   bool HandleSubstringCommand(std::vector<std::string> const& args);
+  bool HandleAppendCommand(std::vector<std::string> const& args);
   bool HandleConcatCommand(std::vector<std::string> const& args);
   bool HandleStripCommand(std::vector<std::string> const& args);
   bool HandleRandomCommand(std::vector<std::string> const& args);
diff --git a/Tests/RunCMake/string/Append.cmake b/Tests/RunCMake/string/Append.cmake
new file mode 100644
index 000000000..2634274bf
--- /dev/null
+++ b/Tests/RunCMake/string/Append.cmake
@@ -0,0 +1,58 @@
+set(out)
+string(APPEND out)
+if(DEFINED out)
+  message(FATAL_ERROR "\"string(APPEND out)\" set out to \"${out}\"")
+endif()
+
+set(out "")
+string(APPEND out)
+if(NOT out STREQUAL "")
+  message(FATAL_ERROR "\"string(APPEND out)\" set out to \"${out}\"")
+endif()
+
+set(out x)
+string(APPEND out)
+if(NOT out STREQUAL "x")
+  message(FATAL_ERROR "\"string(APPEND out)\" set out to \"${out}\"")
+endif()
+
+
+set(out)
+string(APPEND out a)
+if(NOT out STREQUAL "a")
+  message(FATAL_ERROR "\"string(APPEND out a)\" set out to \"${out}\"")
+endif()
+
+set(out "")
+string(APPEND out a)
+if(NOT out STREQUAL "a")
+  message(FATAL_ERROR "\"string(APPEND out a)\" set out to \"${out}\"")
+endif()
+
+set(out x)
+string(APPEND out a)
+if(NOT out STREQUAL "xa")
+  message(FATAL_ERROR "\"string(APPEND out a)\" set out to \"${out}\"")
+endif()
+
+
+set(out x)
+string(APPEND out a "b")
+if(NOT out STREQUAL "xab")
+  message(FATAL_ERROR "\"string(APPEND out a \"b\")\" set out to \"${out}\"")
+endif()
+
+set(b)
+set(out x)
+string(APPEND out ${b})
+if(NOT out STREQUAL "x")
+  message(FATAL_ERROR "\"string(APPEND out \${b})\" set out to \"${out}\"")
+endif()
+
+set(b b)
+set(out x)
+string(APPEND out a "${b}" [[
+${c}]])
+if(NOT out STREQUAL "xab\${c}")
+  message(FATAL_ERROR "\"string(APPEND out a \"\${b}\" [[\${c}]])\" set out to \"${out}\"")
+endif()
diff --git a/Tests/RunCMake/string/AppendNoArgs-result.txt b/Tests/RunCMake/string/AppendNoArgs-result.txt
new file mode 100644
index 000000000..d00491fd7
--- /dev/null
+++ b/Tests/RunCMake/string/AppendNoArgs-result.txt
@@ -0,0 +1 @@
+1
diff --git a/Tests/RunCMake/string/AppendNoArgs-stderr.txt b/Tests/RunCMake/string/AppendNoArgs-stderr.txt
new file mode 100644
index 000000000..75ad427fd
--- /dev/null
+++ b/Tests/RunCMake/string/AppendNoArgs-stderr.txt
@@ -0,0 +1,4 @@
+CMake Error at AppendNoArgs.cmake:1 \(string\):
+  string sub-command APPEND requires at least one argument.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:3 \(include\)
diff --git a/Tests/RunCMake/string/AppendNoArgs.cmake b/Tests/RunCMake/string/AppendNoArgs.cmake
new file mode 100644
index 000000000..f54fb7719
--- /dev/null
+++ b/Tests/RunCMake/string/AppendNoArgs.cmake
@@ -0,0 +1 @@
+string(APPEND)
diff --git a/Tests/RunCMake/string/RunCMakeTest.cmake b/Tests/RunCMake/string/RunCMakeTest.cmake
index 89f7ea517..8067d9dbf 100644
--- a/Tests/RunCMake/string/RunCMakeTest.cmake
+++ b/Tests/RunCMake/string/RunCMakeTest.cmake
@@ -1,5 +1,8 @@
 include(RunCMake)
 
+run_cmake(Append)
+run_cmake(AppendNoArgs)
+
 run_cmake(Concat)
 run_cmake(ConcatNoArgs)