Index: flang/include/flang/Runtime/coarray.h
===================================================================
--- /dev/null
+++ flang/include/flang/Runtime/coarray.h
@@ -0,0 +1,32 @@
+//===-- include/flang/Runtime/coarray.h -------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef FORTRAN_RUNTIME_COARRAY_H_
+#define FORTRAN_RUNTIME_COARRAY_H_
+
+// Defines API between compiled code and the coarray
+// support functions in the runtime library.
+
+#include "flang/Runtime/entry-names.h"
+
+namespace Fortran::runtime {
+
+extern "C" {
+// 16.9.145 NUM_IMAGES
+// The default value team_number=0 is not a valid team number and thus chosen
+// when NUM_IMAGES is called with no actual arguments, see:
+//   1. 9.6 paragraph 3: TEAM_NUMBER shall be from a FORM TEAM statement or
+//      the initial team.
+//   2. 16.9.189 TEAM_NUMBER paragraph 5: initial team shall have the value -1.
+//   3. 11.6.9 FORM TEAM statement: TEAM_NUMBER shall be greater than 0.
+int RTNAME(NumImages)(
+    int team_number = 0, const char *sourceFile = nullptr, int sourceLine = 0);
+}
+} // namespace Fortran::runtime
+
+#endif // FORTRAN_RUNTIME_COARRAY_H_