Index: flang/include/flang/Optimizer/Builder/Runtime/Numeric.h
===================================================================
--- flang/include/flang/Optimizer/Builder/Runtime/Numeric.h
+++ flang/include/flang/Optimizer/Builder/Runtime/Numeric.h
@@ -38,6 +38,10 @@
 mlir::Value genScale(fir::FirOpBuilder &builder, mlir::Location loc,
                      mlir::Value x, mlir::Value i);
 
+/// Generate call to Selected_int_kind intrinsic runtime routine.
+mlir::Value genSelectedIntKind(fir::FirOpBuilder &builder, mlir::Location loc,
+                               mlir::Value x);
+
 /// Generate call to Set_exponent intrinsic runtime routine.
 mlir::Value genSetExponent(fir::FirOpBuilder &builder, mlir::Location loc,
                            mlir::Value x, mlir::Value i);
Index: flang/include/flang/Runtime/numeric.h
===================================================================
--- flang/include/flang/Runtime/numeric.h
+++ flang/include/flang/Runtime/numeric.h
@@ -439,6 +439,20 @@
     CppTypeFor<TypeCategory::Real, 16>, std::int64_t);
 #endif
 
+// SELECTED_INT_KIND
+CppTypeFor<TypeCategory::Integer, 4> RTNAME(SelectedIntKind1)(
+    CppTypeFor<TypeCategory::Integer, 1> x);
+CppTypeFor<TypeCategory::Integer, 4> RTNAME(SelectedIntKind2)(
+    CppTypeFor<TypeCategory::Integer, 2> x);
+CppTypeFor<TypeCategory::Integer, 4> RTNAME(SelectedIntKind4)(
+    CppTypeFor<TypeCategory::Integer, 4> x);
+CppTypeFor<TypeCategory::Integer, 4> RTNAME(SelectedIntKind8)(
+    CppTypeFor<TypeCategory::Integer, 8> x);
+#ifdef __SIZEOF_INT128__
+CppTypeFor<TypeCategory::Integer, 4> RTNAME(SelectedIntKind16)(
+    CppTypeFor<TypeCategory::Integer, 16> x);
+#endif
+
 // SPACING
 CppTypeFor<TypeCategory::Real, 4> RTNAME(Spacing4)(
     CppTypeFor<TypeCategory::Real, 4>);
Index: flang/lib/Lower/IntrinsicCall.cpp
===================================================================
--- flang/lib/Lower/IntrinsicCall.cpp
+++ flang/lib/Lower/IntrinsicCall.cpp
@@ -531,6 +531,7 @@
                            llvm::ArrayRef<mlir::Value> args);
   mlir::Value genScale(mlir::Type, llvm::ArrayRef<mlir::Value>);
   fir::ExtendedValue genScan(mlir::Type, llvm::ArrayRef<fir::ExtendedValue>);
+  mlir::Value genSelectedIntKind(mlir::Type, llvm::ArrayRef<mlir::Value>);
   mlir::Value genSetExponent(mlir::Type resultType,
                              llvm::ArrayRef<mlir::Value> args);
   mlir::Value genSign(mlir::Type, llvm::ArrayRef<mlir::Value>);
@@ -890,6 +891,10 @@
        {"back", asValue, handleDynamicOptional},
        {"kind", asValue}}},
      /*isElemental=*/true},
+    {"selected_int_kind",
+     &I::genSelectedIntKind,
+     {{{"scalar", asValue}}},
+     /*isElemental=*/false},
     {"set_exponent", &I::genSetExponent},
     {"sign", &I::genSign},
     {"size",
@@ -3623,6 +3628,17 @@
   return readAndAddCleanUp(resultMutableBox, resultType, "SCAN");
 }
 
+// SELECTED_INT_KIND
+mlir::Value
+IntrinsicLibrary::genSelectedIntKind(mlir::Type resultType,
+                                     llvm::ArrayRef<mlir::Value> args) {
+  assert(args.size() == 1);
+
+  return builder.createConvert(
+      loc, resultType,
+      fir::runtime::genSelectedIntKind(builder, loc, fir::getBase(args[0])));
+}
+
 // SET_EXPONENT
 mlir::Value IntrinsicLibrary::genSetExponent(mlir::Type resultType,
                                              llvm::ArrayRef<mlir::Value> args) {
Index: flang/lib/Optimizer/Builder/Runtime/Numeric.cpp
===================================================================
--- flang/lib/Optimizer/Builder/Runtime/Numeric.cpp
+++ flang/lib/Optimizer/Builder/Runtime/Numeric.cpp
@@ -160,7 +160,20 @@
   }
 };
 
-/// Placeholder for real*10 version of RRSpacing Intrinsic
+/// Placeholder for integer*16 version of SelectedIntKind Intrinsic
+struct ForcedSelectedIntKind16 {
+  static constexpr const char *name =
+      ExpandAndQuoteKey(RTNAME(SelectedIntKind16));
+  static constexpr fir::runtime::FuncTypeBuilderFunc getTypeModel() {
+    return [](mlir::MLIRContext *ctx) {
+      auto int128Ty = mlir::IntegerType::get(ctx, 128);
+      auto int32Ty = mlir::IntegerType::get(ctx, 32);
+      return mlir::FunctionType::get(ctx, {int128Ty}, {int32Ty});
+    };
+  }
+};
+
+/// Placeholder for real*10 version of SetExponent Intrinsic
 struct ForcedSetExponent10 {
   static constexpr const char *name = ExpandAndQuoteKey(RTNAME(SetExponent10));
   static constexpr fir::runtime::FuncTypeBuilderFunc getTypeModel() {
@@ -172,7 +185,7 @@
   }
 };
 
-/// Placeholder for real*10 version of RRSpacing Intrinsic
+/// Placeholder for real*10 version of SetExponent Intrinsic
 struct ForcedSetExponent16 {
   static constexpr const char *name = ExpandAndQuoteKey(RTNAME(SetExponent16));
   static constexpr fir::runtime::FuncTypeBuilderFunc getTypeModel() {
@@ -360,6 +373,36 @@
   return builder.create<fir::CallOp>(loc, func, args).getResult(0);
 }
 
+/// Generate call to Selected_int_kind intrinsic runtime routine.
+mlir::Value fir::runtime::genSelectedIntKind(fir::FirOpBuilder &builder,
+                                             mlir::Location loc,
+                                             mlir::Value x) {
+  mlir::func::FuncOp func;
+  mlir::Type iTy = x.getType();
+
+  if (iTy.isInteger(8))
+    func =
+        fir::runtime::getRuntimeFunc<mkRTKey(SelectedIntKind1)>(loc, builder);
+  else if (iTy.isInteger(16))
+    func =
+        fir::runtime::getRuntimeFunc<mkRTKey(SelectedIntKind2)>(loc, builder);
+  else if (iTy.isInteger(32))
+    func =
+        fir::runtime::getRuntimeFunc<mkRTKey(SelectedIntKind4)>(loc, builder);
+  else if (iTy.isInteger(64))
+    func =
+        fir::runtime::getRuntimeFunc<mkRTKey(SelectedIntKind8)>(loc, builder);
+  else if (iTy.isInteger(128))
+    func = fir::runtime::getRuntimeFunc<ForcedSelectedIntKind16>(loc, builder);
+  else
+    fir::emitFatalError(loc, "unsupported INTEGER kind in SELECTED_INT_KIND");
+
+  auto funcTy = func.getFunctionType();
+  auto args = fir::runtime::createArguments(builder, loc, funcTy, x);
+
+  return builder.create<fir::CallOp>(loc, func, args).getResult(0);
+}
+
 /// Generate call to Set_exponent instrinsic runtime routine.
 mlir::Value fir::runtime::genSetExponent(fir::FirOpBuilder &builder,
                                          mlir::Location loc, mlir::Value x,
Index: flang/runtime/numeric.cpp
===================================================================
--- flang/runtime/numeric.cpp
+++ flang/runtime/numeric.cpp
@@ -115,6 +115,25 @@
   return std::ldexp(x, p); // x*2**p
 }
 
+// SELECTED_INT_KIND (16.9.169)
+template <typename T>
+inline CppTypeFor<TypeCategory::Integer, 4> SelectedIntKind(T x) {
+  if (x <= 2) {
+    return 1;
+  } else if (x <= 4) {
+    return 2;
+  } else if (x <= 9) {
+    return 4;
+  } else if (x <= 18) {
+    return 8;
+#ifdef __SIZEOF_INT128__
+  } else if (x <= 38) {
+    return 16;
+#endif
+  }
+  return -1;
+}
+
 // SET_EXPONENT (16.9.171)
 template <typename T> inline T SetExponent(T x, std::int64_t p) {
   if (std::isnan(x)) {
@@ -839,6 +858,29 @@
 }
 #endif
 
+CppTypeFor<TypeCategory::Integer, 4> RTNAME(SelectedIntKind1)(
+    CppTypeFor<TypeCategory::Integer, 1> x) {
+  return SelectedIntKind(x);
+}
+CppTypeFor<TypeCategory::Integer, 4> RTNAME(SelectedIntKind2)(
+    CppTypeFor<TypeCategory::Integer, 2> x) {
+  return SelectedIntKind(x);
+}
+CppTypeFor<TypeCategory::Integer, 4> RTNAME(SelectedIntKind4)(
+    CppTypeFor<TypeCategory::Integer, 4> x) {
+  return SelectedIntKind(x);
+}
+CppTypeFor<TypeCategory::Integer, 4> RTNAME(SelectedIntKind8)(
+    CppTypeFor<TypeCategory::Integer, 8> x) {
+  return SelectedIntKind(x);
+}
+#ifdef __SIZEOF_INT128__
+CppTypeFor<TypeCategory::Integer, 4> RTNAME(SelectedIntKind16)(
+    CppTypeFor<TypeCategory::Integer, 16> x) {
+  return SelectedIntKind(x);
+}
+#endif
+
 CppTypeFor<TypeCategory::Real, 4> RTNAME(Spacing4)(
     CppTypeFor<TypeCategory::Real, 4> x) {
   return Spacing<24>(x);
Index: flang/test/Lower/Intrinsics/selected_int_kind.f90
===================================================================
--- /dev/null
+++ flang/test/Lower/Intrinsics/selected_int_kind.f90
@@ -0,0 +1,76 @@
+! REQUIRES: shell
+! RUN: bbc -emit-fir %s -o - | FileCheck %s
+
+! CHECK-LABEL: func.func @_QPselected_int_kind_test1(
+! CHECK-SAME:                                        %[[VAL_0:.*]]: !fir.ref<i8> {fir.bindc_name = "a"}) {
+! CHECK:         %[[VAL_1:.*]] = fir.alloca i8 {bindc_name = "res", uniq_name = "_QFselected_int_kind_test1Eres"}
+! CHECK:         %[[VAL_2:.*]] = fir.load %[[VAL_0]] : !fir.ref<i8>
+! CHECK:         %[[VAL_3:.*]] = fir.call @_FortranASelectedIntKind1(%[[VAL_2]]) : (i8) -> i32
+! CHECK:         %[[VAL_4:.*]] = fir.convert %[[VAL_3]] : (i32) -> i8
+! CHECK:         fir.store %[[VAL_4]] to %[[VAL_1]] : !fir.ref<i8>
+! CHECK:         return
+! CHECK:       }
+
+subroutine selected_int_kind_test1(a)
+  integer(1) :: a, res
+  res = selected_int_kind(a)
+end
+
+! CHECK-LABEL: func.func @_QPselected_int_kind_test2(
+! CHECK-SAME:                                        %[[VAL_0:.*]]: !fir.ref<i16> {fir.bindc_name = "a"}) {
+! CHECK:         %[[VAL_1:.*]] = fir.alloca i16 {bindc_name = "res", uniq_name = "_QFselected_int_kind_test2Eres"}
+! CHECK:         %[[VAL_2:.*]] = fir.load %[[VAL_0]] : !fir.ref<i16>
+! CHECK:         %[[VAL_3:.*]] = fir.call @_FortranASelectedIntKind2(%[[VAL_2]]) : (i16) -> i32
+! CHECK:         %[[VAL_4:.*]] = fir.convert %[[VAL_3]] : (i32) -> i16
+! CHECK:         fir.store %[[VAL_4]] to %[[VAL_1]] : !fir.ref<i16>
+! CHECK:         return
+! CHECK:       }
+
+subroutine selected_int_kind_test2(a)
+  integer(2) :: a, res
+  res = selected_int_kind(a)
+end
+
+! CHECK-LABEL: func.func @_QPselected_int_kind_test4(
+! CHECK-SAME:                                        %[[VAL_0:.*]]: !fir.ref<i32> {fir.bindc_name = "a"}) {
+! CHECK:         %[[VAL_1:.*]] = fir.alloca i32 {bindc_name = "res", uniq_name = "_QFselected_int_kind_test4Eres"}
+! CHECK:         %[[VAL_2:.*]] = fir.load %[[VAL_0]] : !fir.ref<i32>
+! CHECK:         %[[VAL_3:.*]] = fir.call @_FortranASelectedIntKind4(%[[VAL_2]]) : (i32) -> i32
+! CHECK:         fir.store %[[VAL_3]] to %[[VAL_1]] : !fir.ref<i32>
+! CHECK:         return
+! CHECK:       }
+
+subroutine selected_int_kind_test4(a)
+  integer(4) :: a, res
+  res = selected_int_kind(a)
+end
+
+! CHECK-LABEL: func.func @_QPselected_int_kind_test8(
+! CHECK-SAME:                                        %[[VAL_0:.*]]: !fir.ref<i64> {fir.bindc_name = "a"}) {
+! CHECK:         %[[VAL_1:.*]] = fir.alloca i64 {bindc_name = "res", uniq_name = "_QFselected_int_kind_test8Eres"}
+! CHECK:         %[[VAL_2:.*]] = fir.load %[[VAL_0]] : !fir.ref<i64>
+! CHECK:         %[[VAL_3:.*]] = fir.call @_FortranASelectedIntKind8(%[[VAL_2]]) : (i64) -> i32
+! CHECK:         %[[VAL_4:.*]] = fir.convert %[[VAL_3]] : (i32) -> i64
+! CHECK:         fir.store %[[VAL_4]] to %[[VAL_1]] : !fir.ref<i64>
+! CHECK:         return
+! CHECK:       }
+
+subroutine selected_int_kind_test8(a)
+  integer(8) :: a, res
+  res = selected_int_kind(a)
+end
+
+! CHECK-LABEL: func.func @_QPselected_int_kind_test16(
+! CHECK-SAME:                                         %[[VAL_0:.*]]: !fir.ref<i128> {fir.bindc_name = "a"}) {
+! CHECK:         %[[VAL_1:.*]] = fir.alloca i128 {bindc_name = "res", uniq_name = "_QFselected_int_kind_test16Eres"}
+! CHECK:         %[[VAL_2:.*]] = fir.load %[[VAL_0]] : !fir.ref<i128>
+! CHECK:         %[[VAL_3:.*]] = fir.call @_FortranASelectedIntKind16(%[[VAL_2]]) : (i128) -> i32
+! CHECK:         %[[VAL_4:.*]] = fir.convert %[[VAL_3]] : (i32) -> i128
+! CHECK:         fir.store %[[VAL_4]] to %[[VAL_1]] : !fir.ref<i128>
+! CHECK:         return
+! CHECK:       }
+
+subroutine selected_int_kind_test16(a)
+  integer(16) :: a, res
+  res = selected_int_kind(a)
+end
Index: flang/unittests/Runtime/Numeric.cpp
===================================================================
--- flang/unittests/Runtime/Numeric.cpp
+++ flang/unittests/Runtime/Numeric.cpp
@@ -139,6 +139,14 @@
       std::isnan(RTNAME(Scale8)(std::numeric_limits<Real<8>>::quiet_NaN(), 1)));
 }
 
+TEST(Numeric, SelectedIntKind) {
+  EXPECT_EQ(RTNAME(SelectedIntKind1)(Int<1>{1}), 1);
+  EXPECT_EQ(RTNAME(SelectedIntKind2)(Int<2>{3}), 2);
+  EXPECT_EQ(RTNAME(SelectedIntKind4)(Int<4>{8}), 4);
+  EXPECT_EQ(RTNAME(SelectedIntKind8)(Int<8>{10}), 8);
+  EXPECT_EQ(RTNAME(SelectedIntKind8)(Int<8>{-10}), 1);
+}
+
 TEST(Numeric, SetExponent) {
   EXPECT_EQ(RTNAME(SetExponent4)(Real<4>{0}, 0), 0);
   EXPECT_EQ(RTNAME(SetExponent8)(Real<8>{0}, 666), 0);