diff --git a/BUILD.gn b/BUILD.gn
index a1a08410fb..9bd4307655 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -949,6 +949,7 @@ source_set("tint_unittests_msl_writer_src") {
     "src/writer/msl/generator_impl_function_test.cc",
     "src/writer/msl/generator_impl_identifier_test.cc",
     "src/writer/msl/generator_impl_if_test.cc",
+    "src/writer/msl/generator_impl_import_test.cc",
     "src/writer/msl/generator_impl_kill_test.cc",
     "src/writer/msl/generator_impl_loop_test.cc",
     "src/writer/msl/generator_impl_member_accessor_test.cc",
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 43033f904e..fe9486d039 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -509,6 +509,7 @@ if(${TINT_BUILD_MSL_WRITER})
     writer/msl/generator_impl_function_test.cc
     writer/msl/generator_impl_identifier_test.cc
     writer/msl/generator_impl_if_test.cc
+    writer/msl/generator_impl_import_test.cc
     writer/msl/generator_impl_kill_test.cc
     writer/msl/generator_impl_loop_test.cc
     writer/msl/generator_impl_member_accessor_test.cc
diff --git a/src/writer/msl/generator_impl.cc b/src/writer/msl/generator_impl.cc
index 2c6411e462..e9f85d55bc 100644
--- a/src/writer/msl/generator_impl.cc
+++ b/src/writer/msl/generator_impl.cc
@@ -14,6 +14,7 @@
 
 #include "src/writer/msl/generator_impl.h"
 
+#include "spirv/unified1/GLSL.std.450.h"
 #include "src/ast/array_accessor_expression.h"
 #include "src/ast/as_expression.h"
 #include "src/ast/assignment_statement.h"
@@ -477,13 +478,130 @@ bool GeneratorImpl::EmitCall(ast::CallExpression* expr) {
 
     out_ << ")";
   } else {
-    // TODO(dsinclair): Handle imported function
-    error_ = "imported calls not handled yet";
-    return false;
+    return EmitImportFunction(expr);
   }
   return true;
 }
 
+bool GeneratorImpl::EmitImportFunction(ast::CallExpression* expr) {
+  auto* ident = expr->func()->AsIdentifier();
+
+  auto* imp = module_->FindImportByName(ident->path());
+  if (imp == nullptr) {
+    error_ = "unable to find import for " + ident->path();
+    return 0;
+  }
+  auto id = imp->GetIdForMethod(ident->name());
+  if (id == 0) {
+    error_ = "unable to lookup: " + ident->name() + " in " + ident->path();
+  }
+
+  out_ << "metal::";
+  switch (id) {
+    case GLSLstd450Acos:
+    case GLSLstd450Acosh:
+    case GLSLstd450Asin:
+    case GLSLstd450Asinh:
+    case GLSLstd450Atan:
+    case GLSLstd450Atan2:
+    case GLSLstd450Atanh:
+    case GLSLstd450Ceil:
+    case GLSLstd450Cos:
+    case GLSLstd450Cosh:
+    case GLSLstd450Cross:
+    case GLSLstd450Determinant:
+    case GLSLstd450Distance:
+    case GLSLstd450Exp:
+    case GLSLstd450Exp2:
+    case GLSLstd450FAbs:
+    case GLSLstd450FaceForward:
+    case GLSLstd450Floor:
+    case GLSLstd450Fma:
+    case GLSLstd450Fract:
+    case GLSLstd450Length:
+    case GLSLstd450Log:
+    case GLSLstd450Log2:
+    case GLSLstd450Normalize:
+    case GLSLstd450Pow:
+    case GLSLstd450Reflect:
+    case GLSLstd450Round:
+    case GLSLstd450Sin:
+    case GLSLstd450Sinh:
+    case GLSLstd450SmoothStep:
+    case GLSLstd450Sqrt:
+    case GLSLstd450Step:
+    case GLSLstd450Tan:
+    case GLSLstd450Tanh:
+    case GLSLstd450Trunc:
+      out_ << ident->name();
+      break;
+    case GLSLstd450InverseSqrt:
+      out_ << "rsqrt";
+      break;
+    case GLSLstd450FMax:
+    case GLSLstd450NMax:
+      out_ << "fmax";
+      break;
+    case GLSLstd450FMin:
+    case GLSLstd450NMin:
+      out_ << "fmin";
+      break;
+    case GLSLstd450FMix:
+      out_ << "mix";
+      break;
+    case GLSLstd450FSign:
+      out_ << "sign";
+      break;
+    case GLSLstd450SAbs:
+      out_ << "abs";
+      break;
+    case GLSLstd450SMax:
+    case GLSLstd450UMax:
+      out_ << "max";
+      break;
+    case GLSLstd450SMin:
+    case GLSLstd450UMin:
+      out_ << "min";
+      break;
+    case GLSLstd450FClamp:
+    case GLSLstd450SClamp:
+    case GLSLstd450NClamp:
+    case GLSLstd450UClamp:
+      out_ << "clamp";
+      break;
+    // TODO(dsinclair): Determine mappings for the following
+    case GLSLstd450Degrees:
+    case GLSLstd450FindILsb:
+    case GLSLstd450FindUMsb:
+    case GLSLstd450FindSMsb:
+    case GLSLstd450InterpolateAtCentroid:
+    case GLSLstd450MatrixInverse:
+    case GLSLstd450Radians:
+    case GLSLstd450RoundEven:
+    case GLSLstd450SSign:
+    default:
+      error_ = "Unknown import method: " + ident->name();
+      return false;
+  }
+
+  out_ << "(";
+  bool first = true;
+  const auto& params = expr->params();
+  for (const auto& param : params) {
+    if (!first) {
+      out_ << ", ";
+    }
+    first = false;
+
+    if (!EmitExpression(param.get())) {
+      return false;
+    }
+  }
+  out_ << ")";
+
+  return true;
+}
+
 bool GeneratorImpl::EmitCase(ast::CaseStatement* stmt) {
   make_indent();
 
diff --git a/src/writer/msl/generator_impl.h b/src/writer/msl/generator_impl.h
index 5578a6226f..cc7d33ad1a 100644
--- a/src/writer/msl/generator_impl.h
+++ b/src/writer/msl/generator_impl.h
@@ -83,7 +83,7 @@ class GeneratorImpl : public TextGenerator {
   bool EmitCall(ast::CallExpression* expr);
   /// Handles a case statement
   /// @param stmt the statement
-  /// @returns true if the statment was emitted successfully
+  /// @returns true if the statement was emitted successfully
   bool EmitCase(ast::CaseStatement* stmt);
   /// Handles generating a cast expression
   /// @param expr the cast expression
@@ -128,12 +128,16 @@ class GeneratorImpl : public TextGenerator {
                             const std::string& ep_name);
   /// Handles generating an identifier expression
   /// @param expr the identifier expression
-  /// @returns true if the identifeir was emitted
+  /// @returns true if the identifier was emitted
   bool EmitIdentifier(ast::IdentifierExpression* expr);
   /// Handles an if statement
   /// @param stmt the statement to emit
   /// @returns true if the statement was successfully emitted
   bool EmitIf(ast::IfStatement* stmt);
+  /// Handles genreating an import expression
+  /// @param expr the expression
+  /// @returns true if the expression was successfully emitted.
+  bool EmitImportFunction(ast::CallExpression* expr);
   /// Handles generating a kill statement
   /// @param stmt the kill statement
   /// @returns true if the statement was successfully emitted
@@ -144,7 +148,7 @@ class GeneratorImpl : public TextGenerator {
   bool EmitLiteral(ast::Literal* lit);
   /// Handles a loop statement
   /// @param stmt the statement to emit
-  /// @returns true if the statement was emtited
+  /// @returns true if the statement was emitted
   bool EmitLoop(ast::LoopStatement* stmt);
   /// Handles a member accessor expression
   /// @param expr the member accessor expression
diff --git a/src/writer/msl/generator_impl_import_test.cc b/src/writer/msl/generator_impl_import_test.cc
new file mode 100644
index 0000000000..fcf0d50b02
--- /dev/null
+++ b/src/writer/msl/generator_impl_import_test.cc
@@ -0,0 +1,361 @@
+// Copyright 2020 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "gtest/gtest.h"
+#include "src/ast/call_expression.h"
+#include "src/ast/float_literal.h"
+#include "src/ast/identifier_expression.h"
+#include "src/ast/module.h"
+#include "src/ast/scalar_constructor_expression.h"
+#include "src/ast/sint_literal.h"
+#include "src/ast/type/f32_type.h"
+#include "src/ast/type/i32_type.h"
+#include "src/ast/type/matrix_type.h"
+#include "src/ast/type/vector_type.h"
+#include "src/ast/type_constructor_expression.h"
+#include "src/context.h"
+#include "src/type_determiner.h"
+#include "src/writer/msl/generator_impl.h"
+
+namespace tint {
+namespace writer {
+namespace msl {
+namespace {
+
+using MslGeneratorImplTest = testing::Test;
+
+struct MslImportData {
+  const char* name;
+  const char* msl_name;
+};
+inline std::ostream& operator<<(std::ostream& out, MslImportData data) {
+  out << data.name;
+  return out;
+}
+using MslImportData_SingleParamTest = testing::TestWithParam<MslImportData>;
+TEST_P(MslImportData_SingleParamTest, FloatScalar) {
+  auto param = GetParam();
+
+  ast::type::F32Type f32;
+
+  ast::ExpressionList params;
+  params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::FloatLiteral>(&f32, 1.f)));
+
+  ast::CallExpression expr(std::make_unique<ast::IdentifierExpression>(
+                               std::vector<std::string>{"std", param.name}),
+                           std::move(params));
+
+  Context ctx;
+  ast::Module mod;
+  TypeDeterminer td(&ctx, &mod);
+  mod.AddImport(std::make_unique<ast::Import>("GLSL.std.450", "std"));
+
+  ASSERT_TRUE(td.DetermineResultType(&expr)) << td.error();
+
+  GeneratorImpl g(&mod);
+  ASSERT_TRUE(g.EmitImportFunction(&expr)) << g.error();
+  EXPECT_EQ(g.result(),
+            std::string("metal::") + param.msl_name + "(1.00000000f)");
+}
+INSTANTIATE_TEST_SUITE_P(MslGeneratorImplTest,
+                         MslImportData_SingleParamTest,
+                         testing::Values(MslImportData{"acos", "acos"},
+                                         MslImportData{"acosh", "acosh"},
+                                         MslImportData{"asin", "asin"},
+                                         MslImportData{"asinh", "asinh"},
+                                         MslImportData{"atan", "atan"},
+                                         MslImportData{"atanh", "atanh"},
+                                         MslImportData{"cos", "cos"},
+                                         MslImportData{"cosh", "cosh"},
+                                         MslImportData{"ceil", "ceil"},
+                                         MslImportData{"exp", "exp"},
+                                         MslImportData{"exp2", "exp2"},
+                                         MslImportData{"fabs", "fabs"},
+                                         MslImportData{"floor", "floor"},
+                                         MslImportData{"fract", "fract"},
+                                         MslImportData{"inversesqrt", "rsqrt"},
+                                         MslImportData{"length", "length"},
+                                         MslImportData{"log", "log"},
+                                         MslImportData{"log2", "log2"},
+                                         MslImportData{"normalize",
+                                                       "normalize"},
+                                         MslImportData{"round", "round"},
+                                         MslImportData{"fsign", "sign"},
+                                         MslImportData{"sin", "sin"},
+                                         MslImportData{"sinh", "sinh"},
+                                         MslImportData{"sqrt", "sqrt"},
+                                         MslImportData{"tan", "tan"},
+                                         MslImportData{"tanh", "tanh"},
+                                         MslImportData{"trunc", "trunc"}));
+
+TEST_F(MslGeneratorImplTest, MslImportData_SingleParamTest_IntScalar) {
+  ast::type::I32Type i32;
+
+  ast::ExpressionList params;
+  params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::SintLiteral>(&i32, 1)));
+
+  ast::CallExpression expr(std::make_unique<ast::IdentifierExpression>(
+                               std::vector<std::string>{"std", "sabs"}),
+                           std::move(params));
+
+  Context ctx;
+  ast::Module mod;
+  TypeDeterminer td(&ctx, &mod);
+  mod.AddImport(std::make_unique<ast::Import>("GLSL.std.450", "std"));
+
+  ASSERT_TRUE(td.DetermineResultType(&expr)) << td.error();
+
+  GeneratorImpl g(&mod);
+  ASSERT_TRUE(g.EmitImportFunction(&expr)) << g.error();
+  EXPECT_EQ(g.result(), R"(metal::abs(1))");
+}
+
+using MslImportData_DualParamTest = testing::TestWithParam<MslImportData>;
+TEST_P(MslImportData_DualParamTest, FloatScalar) {
+  auto param = GetParam();
+
+  ast::type::F32Type f32;
+
+  ast::ExpressionList params;
+  params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::FloatLiteral>(&f32, 1.f)));
+  params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::FloatLiteral>(&f32, 2.f)));
+
+  ast::CallExpression expr(std::make_unique<ast::IdentifierExpression>(
+                               std::vector<std::string>{"std", param.name}),
+                           std::move(params));
+
+  Context ctx;
+  ast::Module mod;
+  TypeDeterminer td(&ctx, &mod);
+  mod.AddImport(std::make_unique<ast::Import>("GLSL.std.450", "std"));
+
+  ASSERT_TRUE(td.DetermineResultType(&expr)) << td.error();
+
+  GeneratorImpl g(&mod);
+  ASSERT_TRUE(g.EmitImportFunction(&expr)) << g.error();
+  EXPECT_EQ(g.result(), std::string("metal::") + param.msl_name +
+                            "(1.00000000f, 2.00000000f)");
+}
+INSTANTIATE_TEST_SUITE_P(MslGeneratorImplTest,
+                         MslImportData_DualParamTest,
+                         testing::Values(MslImportData{"atan2", "atan2"},
+                                         MslImportData{"distance", "distance"},
+                                         MslImportData{"fmax", "fmax"},
+                                         MslImportData{"fmin", "fmin"},
+                                         MslImportData{"nmax", "fmax"},
+                                         MslImportData{"nmin", "fmin"},
+                                         MslImportData{"pow", "pow"},
+                                         MslImportData{"reflect", "reflect"},
+                                         MslImportData{"step", "step"}));
+
+using MslImportData_DualParam_VectorTest =
+    testing::TestWithParam<MslImportData>;
+TEST_P(MslImportData_DualParam_VectorTest, FloatVector) {
+  auto param = GetParam();
+
+  ast::type::F32Type f32;
+  ast::type::VectorType vec(&f32, 3);
+
+  ast::ExpressionList type_params;
+  type_params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::FloatLiteral>(&f32, 1.f)));
+  type_params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::FloatLiteral>(&f32, 2.f)));
+  type_params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::FloatLiteral>(&f32, 3.f)));
+
+  ast::ExpressionList params;
+  params.push_back(std::make_unique<ast::TypeConstructorExpression>(
+      &vec, std::move(type_params)));
+
+  type_params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::FloatLiteral>(&f32, 4.f)));
+  type_params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::FloatLiteral>(&f32, 5.f)));
+  type_params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::FloatLiteral>(&f32, 6.f)));
+  params.push_back(std::make_unique<ast::TypeConstructorExpression>(
+      &vec, std::move(type_params)));
+
+  ast::CallExpression expr(std::make_unique<ast::IdentifierExpression>(
+                               std::vector<std::string>{"std", param.name}),
+                           std::move(params));
+
+  Context ctx;
+  ast::Module mod;
+  TypeDeterminer td(&ctx, &mod);
+  mod.AddImport(std::make_unique<ast::Import>("GLSL.std.450", "std"));
+
+  ASSERT_TRUE(td.DetermineResultType(&expr)) << td.error();
+
+  GeneratorImpl g(&mod);
+  ASSERT_TRUE(g.EmitImportFunction(&expr)) << g.error();
+  EXPECT_EQ(g.result(), std::string("metal::") + param.msl_name +
+                            "(float3(1.00000000f, 2.00000000f, 3.00000000f), "
+                            "float3(4.00000000f, 5.00000000f, 6.00000000f))");
+}
+INSTANTIATE_TEST_SUITE_P(MslGeneratorImplTest,
+                         MslImportData_DualParam_VectorTest,
+                         testing::Values(MslImportData{"cross", "cross"}));
+
+using MslImportData_DualParam_Int_Test = testing::TestWithParam<MslImportData>;
+TEST_P(MslImportData_DualParam_Int_Test, IntScalar) {
+  auto param = GetParam();
+
+  ast::type::I32Type i32;
+
+  ast::ExpressionList params;
+  params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::SintLiteral>(&i32, 1)));
+  params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::SintLiteral>(&i32, 2)));
+
+  ast::CallExpression expr(std::make_unique<ast::IdentifierExpression>(
+                               std::vector<std::string>{"std", param.name}),
+                           std::move(params));
+
+  Context ctx;
+  ast::Module mod;
+  TypeDeterminer td(&ctx, &mod);
+  mod.AddImport(std::make_unique<ast::Import>("GLSL.std.450", "std"));
+
+  ASSERT_TRUE(td.DetermineResultType(&expr)) << td.error();
+
+  GeneratorImpl g(&mod);
+  ASSERT_TRUE(g.EmitImportFunction(&expr)) << g.error();
+  EXPECT_EQ(g.result(), std::string("metal::") + param.msl_name + "(1, 2)");
+}
+INSTANTIATE_TEST_SUITE_P(MslGeneratorImplTest,
+                         MslImportData_DualParam_Int_Test,
+                         testing::Values(MslImportData{"smax", "max"},
+                                         MslImportData{"smin", "min"},
+                                         MslImportData{"umax", "max"},
+                                         MslImportData{"umin", "min"}));
+
+using MslImportData_TripleParamTest = testing::TestWithParam<MslImportData>;
+TEST_P(MslImportData_TripleParamTest, FloatScalar) {
+  auto param = GetParam();
+
+  ast::type::F32Type f32;
+
+  ast::ExpressionList params;
+  params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::FloatLiteral>(&f32, 1.f)));
+  params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::FloatLiteral>(&f32, 2.f)));
+  params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::FloatLiteral>(&f32, 3.f)));
+
+  ast::CallExpression expr(std::make_unique<ast::IdentifierExpression>(
+                               std::vector<std::string>{"std", param.name}),
+                           std::move(params));
+
+  Context ctx;
+  ast::Module mod;
+  TypeDeterminer td(&ctx, &mod);
+  mod.AddImport(std::make_unique<ast::Import>("GLSL.std.450", "std"));
+
+  ASSERT_TRUE(td.DetermineResultType(&expr)) << td.error();
+
+  GeneratorImpl g(&mod);
+  ASSERT_TRUE(g.EmitImportFunction(&expr)) << g.error();
+  EXPECT_EQ(g.result(), std::string("metal::") + param.msl_name +
+                            "(1.00000000f, 2.00000000f, 3.00000000f)");
+}
+INSTANTIATE_TEST_SUITE_P(
+    MslGeneratorImplTest,
+    MslImportData_TripleParamTest,
+    testing::Values(MslImportData{"faceforward", "faceforward"},
+                    MslImportData{"fma", "fma"},
+                    MslImportData{"fclamp", "clamp"},
+                    MslImportData{"fmix", "mix"},
+                    MslImportData{"nclamp", "clamp"},
+                    MslImportData{"smoothstep", "smoothstep"}));
+
+using MslImportData_TripleParam_Int_Test =
+    testing::TestWithParam<MslImportData>;
+TEST_P(MslImportData_TripleParam_Int_Test, IntScalar) {
+  auto param = GetParam();
+
+  ast::type::I32Type i32;
+
+  ast::ExpressionList params;
+  params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::SintLiteral>(&i32, 1)));
+  params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::SintLiteral>(&i32, 2)));
+  params.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::SintLiteral>(&i32, 3)));
+
+  ast::CallExpression expr(std::make_unique<ast::IdentifierExpression>(
+                               std::vector<std::string>{"std", param.name}),
+                           std::move(params));
+
+  Context ctx;
+  ast::Module mod;
+  TypeDeterminer td(&ctx, &mod);
+  mod.AddImport(std::make_unique<ast::Import>("GLSL.std.450", "std"));
+
+  ASSERT_TRUE(td.DetermineResultType(&expr)) << td.error();
+
+  GeneratorImpl g(&mod);
+  ASSERT_TRUE(g.EmitImportFunction(&expr)) << g.error();
+  EXPECT_EQ(g.result(), std::string("metal::") + param.msl_name + "(1, 2, 3)");
+}
+INSTANTIATE_TEST_SUITE_P(MslGeneratorImplTest,
+                         MslImportData_TripleParam_Int_Test,
+                         testing::Values(MslImportData{"sclamp", "clamp"},
+                                         MslImportData{"uclamp", "clamp"}));
+
+TEST_F(MslGeneratorImplTest, MslImportData_Determinant) {
+  ast::type::F32Type f32;
+  ast::type::MatrixType mat(&f32, 3, 3);
+
+  auto var = std::make_unique<ast::Variable>(
+      "var", ast::StorageClass::kFunction, &mat);
+
+  ast::ExpressionList params;
+  params.push_back(std::make_unique<ast::IdentifierExpression>("var"));
+
+  ast::CallExpression expr(std::make_unique<ast::IdentifierExpression>(
+                               std::vector<std::string>{"std", "determinant"}),
+                           std::move(params));
+
+  Context ctx;
+  ast::Module mod;
+  mod.AddGlobalVariable(std::move(var));
+  mod.AddImport(std::make_unique<ast::Import>("GLSL.std.450", "std"));
+
+  TypeDeterminer td(&ctx, &mod);
+  // Register the global
+  ASSERT_TRUE(td.Determine()) << td.error();
+  ASSERT_TRUE(td.DetermineResultType(&expr)) << td.error();
+
+  GeneratorImpl g(&mod);
+  ASSERT_TRUE(g.EmitImportFunction(&expr)) << g.error();
+  EXPECT_EQ(g.result(), std::string("metal::determinant(var)"));
+}
+
+}  // namespace
+}  // namespace msl
+}  // namespace writer
+}  // namespace tint