Index: flang/lib/Evaluate/intrinsics.cpp
===================================================================
--- flang/lib/Evaluate/intrinsics.cpp
+++ flang/lib/Evaluate/intrinsics.cpp
@@ -581,6 +581,10 @@
         Rank::dimReduced, IntrinsicClass::transformationalFunction},
     {"not", {{"i", SameInt}}, SameInt},
     // NULL() is a special case handled in Probe() below
+    {"num_images", {}, DefaultInt, Rank::scalar,
+        IntrinsicClass::transformationalFunction},
+    {"num_images", {{"team_number", AnyInt, Rank::scalar}}, DefaultInt,
+        Rank::scalar, IntrinsicClass::transformationalFunction},
     {"out_of_range",
         {{"x", AnyIntOrReal}, {"mold", AnyIntOrReal, Rank::scalar}},
         DefaultLogical},
@@ -724,7 +728,7 @@
 
 // TODO: Coarray intrinsic functions
 //   LCOBOUND, UCOBOUND, FAILED_IMAGES, GET_TEAM, IMAGE_INDEX,
-//   NUM_IMAGES, STOPPED_IMAGES, TEAM_NUMBER, THIS_IMAGE,
+//   STOPPED_IMAGES, TEAM_NUMBER, THIS_IMAGE,
 //   COSHAPE
 // TODO: Non-standard intrinsic functions
 //  AND, OR, XOR, LSHIFT, RSHIFT, SHIFT, ZEXT, IZEXT,
Index: flang/test/Semantics/call10.f90
===================================================================
--- flang/test/Semantics/call10.f90
+++ flang/test/Semantics/call10.f90
@@ -185,7 +185,10 @@
                                    ! implicit sync all
     !ERROR: Procedure 'this_image' referenced in pure subprogram 's14' must be pure too
     img = this_image()
-    !ERROR: Procedure 'num_images' referenced in pure subprogram 's14' must be pure too
+
+    ! num_images() is now evaluted as an intrinsic function
+    ! no longer produces an error because
+    ! "All standard intrinsic functions are pure" - 16.1 of the Fortran Standard 2018
     nimgs = num_images()
     i = img                       ! i is ready to use
 
Index: flang/test/Semantics/num_images.f90
===================================================================
--- /dev/null
+++ flang/test/Semantics/num_images.f90
@@ -0,0 +1,30 @@
+! RUN: %S/test_errors.sh %s %t %f18
+! Check for semantic errors in num_images() function calls
+
+subroutine test
+
+  ! correct calls, should produce no errors
+  print *, num_images()
+  print *, num_images(team_number=1)
+  print *, num_images(1)
+
+  ! incorrectly typed argument
+  ! the error is seen as too many arguments to the num_images() call with no arguments
+  !ERROR: too many actual arguments for intrinsic 'num_images'
+  print *, num_images(3.4)
+
+  ! call with too many arguments
+  !ERROR: too many actual arguments for intrinsic 'num_images'
+  print *, num_images(1, 1)
+
+  ! keyword argument with incorrect type
+  !ERROR: unknown keyword argument to intrinsic 'num_images'
+  print *, num_images(team_number=3.4)
+
+  ! incorrect keyword argument
+  !ERROR: unknown keyword argument to intrinsic 'num_images'
+  print *, num_images(team_numbers=1)
+
+  !TODO: test num_images() calls related to team_type argument
+
+end subroutine
Index: flang/unittests/Evaluate/intrinsics.cpp
===================================================================
--- flang/unittests/Evaluate/intrinsics.cpp
+++ flang/unittests/Evaluate/intrinsics.cpp
@@ -257,6 +257,40 @@
   TestCall{defaults, table, "idint"}
       .Push(Const(Scalar<Real4>{}))
       .DoCall(Int4::GetType());
+
+  TestCall{defaults, table, "num_images"}.DoCall(Int4::GetType());
+  TestCall{defaults, table, "num_images"}
+      .Push(Const(Scalar<Int1>{}))
+      .DoCall(Int4::GetType());
+  TestCall{defaults, table, "num_images"}
+      .Push(Const(Scalar<Int4>{}))
+      .DoCall(Int4::GetType());
+  TestCall{defaults, table, "num_images"}
+      .Push(Const(Scalar<Int8>{}))
+      .DoCall(Int4::GetType());
+  TestCall{defaults, table, "num_images"}
+      .Push(Named("team_number", Const(Scalar<Int4>{})))
+      .DoCall(Int4::GetType());
+  TestCall{defaults, table, "num_images"}
+      .Push(Const(Scalar<Int4>{}))
+      .Push(Const(Scalar<Int4>{}))
+      .DoCall(); // too many args
+  TestCall{defaults, table, "num_images"}
+      .Push(Named("bad", Const(Scalar<Int4>{})))
+      .DoCall(); // bad keyword
+  TestCall{defaults, table, "num_images"}
+      .Push(Const(Scalar<Char>{}))
+      .DoCall(); // bad type
+  TestCall{defaults, table, "num_images"}
+      .Push(Const(Scalar<Log4>{}))
+      .DoCall(); // bad type
+  TestCall{defaults, table, "num_images"}
+      .Push(Const(Scalar<Complex8>{}))
+      .DoCall(); // bad type
+  TestCall{defaults, table, "num_images"}
+      .Push(Const(Scalar<Real4>{}))
+      .DoCall(); // bad type
+
   // TODO: test other intrinsics
 }
 } // namespace Fortran::evaluate