diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 8f45236..d0b678c 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -408,10 +408,11 @@
 if(${TINT_BUILD_SPV_WRITER})
   list(APPEND TINT_TEST_SRCS
     writer/spirv/binary_writer_test.cc
-    writer/spirv/builder_test.cc
     writer/spirv/builder_entry_point_test.cc
     writer/spirv/builder_function_test.cc
+    writer/spirv/builder_global_variable_test.cc
     writer/spirv/builder_literal_test.cc
+    writer/spirv/builder_test.cc
     writer/spirv/builder_type_test.cc
     writer/spirv/instruction_test.cc
     writer/spirv/operand_test.cc
diff --git a/src/ast/binding_decoration.cc b/src/ast/binding_decoration.cc
index d9532fe..a2fbc0c 100644
--- a/src/ast/binding_decoration.cc
+++ b/src/ast/binding_decoration.cc
@@ -17,7 +17,7 @@
 namespace tint {
 namespace ast {
 
-BindingDecoration::BindingDecoration(size_t val) : value_(val) {}
+BindingDecoration::BindingDecoration(uint32_t val) : value_(val) {}
 
 BindingDecoration::~BindingDecoration() = default;
 
diff --git a/src/ast/binding_decoration.h b/src/ast/binding_decoration.h
index 1a7e573..b9484a5 100644
--- a/src/ast/binding_decoration.h
+++ b/src/ast/binding_decoration.h
@@ -27,21 +27,21 @@
  public:
   /// constructor
   /// @param value the binding value
-  explicit BindingDecoration(size_t value);
+  explicit BindingDecoration(uint32_t value);
   ~BindingDecoration() override;
 
   /// @returns true if this is a binding decoration
   bool IsBinding() const override { return true; }
 
   /// @returns the binding value
-  size_t value() const { return value_; }
+  uint32_t value() const { return value_; }
 
   /// Outputs the decoration to the given stream
   /// @param out the stream to output too
   void to_str(std::ostream& out) const override;
 
  private:
-  size_t value_;
+  uint32_t value_;
 };
 
 }  // namespace ast
diff --git a/src/ast/location_decoration.cc b/src/ast/location_decoration.cc
index 9fb8d5f..f261b3a 100644
--- a/src/ast/location_decoration.cc
+++ b/src/ast/location_decoration.cc
@@ -17,7 +17,7 @@
 namespace tint {
 namespace ast {
 
-LocationDecoration::LocationDecoration(size_t val) : value_(val) {}
+LocationDecoration::LocationDecoration(uint32_t val) : value_(val) {}
 
 LocationDecoration::~LocationDecoration() = default;
 
diff --git a/src/ast/location_decoration.h b/src/ast/location_decoration.h
index 69b61dc..287e891 100644
--- a/src/ast/location_decoration.h
+++ b/src/ast/location_decoration.h
@@ -27,21 +27,21 @@
  public:
   /// constructor
   /// @param value the location value
-  explicit LocationDecoration(size_t value);
+  explicit LocationDecoration(uint32_t value);
   ~LocationDecoration() override;
 
   /// @returns true if this is a location decoration
   bool IsLocation() const override { return true; }
 
   /// @returns the location value
-  size_t value() const { return value_; }
+  uint32_t value() const { return value_; }
 
   /// Outputs the decoration to the given stream
   /// @param out the stream to output too
   void to_str(std::ostream& out) const override;
 
  private:
-  size_t value_;
+  uint32_t value_;
 };
 
 }  // namespace ast
diff --git a/src/ast/set_decoration.cc b/src/ast/set_decoration.cc
index 7d54d98..6d965a2 100644
--- a/src/ast/set_decoration.cc
+++ b/src/ast/set_decoration.cc
@@ -17,7 +17,7 @@
 namespace tint {
 namespace ast {
 
-SetDecoration::SetDecoration(size_t val) : value_(val) {}
+SetDecoration::SetDecoration(uint32_t val) : value_(val) {}
 
 SetDecoration::~SetDecoration() = default;
 
diff --git a/src/ast/set_decoration.h b/src/ast/set_decoration.h
index 253e940..dd0e2d9 100644
--- a/src/ast/set_decoration.h
+++ b/src/ast/set_decoration.h
@@ -27,21 +27,21 @@
  public:
   /// constructor
   /// @param value the set value
-  explicit SetDecoration(size_t value);
+  explicit SetDecoration(uint32_t value);
   ~SetDecoration() override;
 
   /// @returns true if this is a set decoration
   bool IsSet() const override { return true; }
 
   /// @returns the set value
-  size_t value() const { return value_; }
+  uint32_t value() const { return value_; }
 
   /// Outputs the decoration to the given stream
   /// @param out the stream to output too
   void to_str(std::ostream& out) const override;
 
  private:
-  size_t value_;
+  uint32_t value_;
 };
 
 }  // namespace ast
diff --git a/src/writer/spirv/builder.cc b/src/writer/spirv/builder.cc
index 5820bf2..7896ae0 100644
--- a/src/writer/spirv/builder.cc
+++ b/src/writer/spirv/builder.cc
@@ -16,9 +16,14 @@
 #include <utility>
 
 #include "spirv/unified1/spirv.h"
+#include "src/ast/binding_decoration.h"
 #include "src/ast/bool_literal.h"
+#include "src/ast/builtin_decoration.h"
+#include "src/ast/decorated_variable.h"
 #include "src/ast/float_literal.h"
 #include "src/ast/int_literal.h"
+#include "src/ast/location_decoration.h"
+#include "src/ast/set_decoration.h"
 #include "src/ast/struct.h"
 #include "src/ast/struct_member.h"
 #include "src/ast/struct_member_offset_decoration.h"
@@ -82,6 +87,12 @@
                 {Operand::Int(SpvAddressingModelLogical),
                  Operand::Int(SpvMemoryModelVulkanKHR)});
 
+  for (const auto& var : m.global_variables()) {
+    if (!GenerateGlobalVariable(var.get())) {
+      return false;
+    }
+  }
+
   for (const auto& func : m.functions()) {
     if (!GenerateFunction(func.get())) {
       return false;
@@ -208,6 +219,60 @@
   return func_type_id;
 }
 
+bool Builder::GenerateGlobalVariable(ast::Variable* var) {
+  auto result = result_op();
+  auto var_id = result.to_i();
+
+  if (var->is_const()) {
+    // TODO(dsinclair): Handle const variables
+    return false;
+  }
+
+  auto sc = var->storage_class() == ast::StorageClass::kNone
+                ? ast::StorageClass::kPrivate
+                : var->storage_class();
+
+  ast::type::PointerType pt(var->type(), sc);
+  auto type_id = GenerateTypeIfNeeded(&pt);
+  if (type_id == 0) {
+    return false;
+  }
+
+  // TODO(dsinclair): Handle variable initializer
+  push_debug(spv::Op::OpName,
+             {Operand::Int(var_id), Operand::String(var->name())});
+  push_type(spv::Op::OpVariable, {Operand::Int(type_id), result,
+                                  Operand::Int(ConvertStorageClass(sc))});
+
+  if (var->IsDecorated()) {
+    for (const auto& deco : var->AsDecorated()->decorations()) {
+      if (deco->IsBuiltin()) {
+        push_debug(spv::Op::OpDecorate,
+                   {Operand::Int(var_id), Operand::Int(SpvDecorationBuiltIn),
+                    Operand::Int(ConvertBuiltin(deco->AsBuiltin()->value()))});
+      } else if (deco->IsLocation()) {
+        push_debug(spv::Op::OpDecorate,
+                   {Operand::Int(var_id), Operand::Int(SpvDecorationLocation),
+                    Operand::Int(deco->AsLocation()->value())});
+      } else if (deco->IsBinding()) {
+        push_debug(spv::Op::OpDecorate,
+                   {Operand::Int(var_id), Operand::Int(SpvDecorationBinding),
+                    Operand::Int(deco->AsBinding()->value())});
+      } else if (deco->IsSet()) {
+        push_debug(
+            spv::Op::OpDecorate,
+            {Operand::Int(var_id), Operand::Int(SpvDecorationDescriptorSet),
+             Operand::Int(deco->AsSet()->value())});
+      } else {
+        error_ = "unknown decoration";
+        return false;
+      }
+    }
+  }
+
+  return true;
+}
+
 void Builder::GenerateImport(ast::Import* imp) {
   auto result = result_op();
   auto id = result.to_i();
@@ -353,6 +418,7 @@
 
   auto stg_class = ConvertStorageClass(ptr->storage_class());
   if (stg_class == SpvStorageClassMax) {
+    error_ = "invalid storage class for pointer";
     return false;
   }
 
@@ -460,6 +526,36 @@
   return SpvStorageClassMax;
 }
 
+SpvBuiltIn Builder::ConvertBuiltin(ast::Builtin builtin) const {
+  switch (builtin) {
+    case ast::Builtin::kPosition:
+      return SpvBuiltInPosition;
+    case ast::Builtin::kVertexIdx:
+      return SpvBuiltInVertexIndex;
+    case ast::Builtin::kInstanceIdx:
+      return SpvBuiltInInstanceIndex;
+    case ast::Builtin::kFrontFacing:
+      return SpvBuiltInFrontFacing;
+    case ast::Builtin::kFragCoord:
+      return SpvBuiltInFragCoord;
+    case ast::Builtin::kFragDepth:
+      return SpvBuiltInFragDepth;
+    case ast::Builtin::kNumWorkgroups:
+      return SpvBuiltInNumWorkgroups;
+    case ast::Builtin::kWorkgroupSize:
+      return SpvBuiltInWorkgroupSize;
+    case ast::Builtin::kLocalInvocationId:
+      return SpvBuiltInLocalInvocationId;
+    case ast::Builtin::kLocalInvocationIdx:
+      return SpvBuiltInLocalInvocationIndex;
+    case ast::Builtin::kGlobalInvocationId:
+      return SpvBuiltInGlobalInvocationId;
+    case ast::Builtin::kNone:
+      break;
+  }
+  return SpvBuiltInMax;
+}
+
 }  // namespace spirv
 }  // namespace writer
 }  // namespace tint
diff --git a/src/writer/spirv/builder.h b/src/writer/spirv/builder.h
index 8aefe56..6c4437e 100644
--- a/src/writer/spirv/builder.h
+++ b/src/writer/spirv/builder.h
@@ -21,6 +21,7 @@
 #include <vector>
 
 #include "spirv/unified1/spirv.h"
+#include "src/ast/builtin.h"
 #include "src/ast/literal.h"
 #include "src/ast/module.h"
 #include "src/ast/struct_member.h"
@@ -127,6 +128,10 @@
   /// @param klass the storage class to convert
   /// @returns the SPIR-V storage class or SpvStorageClassMax on error.
   SpvStorageClass ConvertStorageClass(ast::StorageClass klass) const;
+  /// Converts a builtin to a SPIR-V builtin
+  /// @param builtin the builtin to convert
+  /// @returns the SPIR-V builtin or SpvBuiltInMax on error.
+  SpvBuiltIn ConvertBuiltin(ast::Builtin builtin) const;
 
   /// Generates an entry point instruction
   /// @param ep the entry point
@@ -140,6 +145,10 @@
   /// @param func the function to generate for
   /// @returns the ID to use for the function type. Returns 0 on failure.
   uint32_t GenerateFunctionTypeIfNeeded(ast::Function* func);
+  /// Generates a global variable
+  /// @param var the variable to generate
+  /// @returns true if the variable is emited.
+  bool GenerateGlobalVariable(ast::Variable* var);
   /// Generates an import instruction
   /// @param imp the import
   void GenerateImport(ast::Import* imp);
diff --git a/src/writer/spirv/builder_global_variable_test.cc b/src/writer/spirv/builder_global_variable_test.cc
new file mode 100644
index 0000000..693ea93
--- /dev/null
+++ b/src/writer/spirv/builder_global_variable_test.cc
@@ -0,0 +1,177 @@
+// 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 "gtest/gtest.h"
+#include "src/ast/binding_decoration.h"
+#include "src/ast/builtin.h"
+#include "src/ast/builtin_decoration.h"
+#include "src/ast/decorated_variable.h"
+#include "src/ast/location_decoration.h"
+#include "src/ast/set_decoration.h"
+#include "src/ast/storage_class.h"
+#include "src/ast/type/f32_type.h"
+#include "src/ast/variable.h"
+#include "src/ast/variable_decoration.h"
+#include "src/writer/spirv/builder.h"
+#include "src/writer/spirv/spv_dump.h"
+
+namespace tint {
+namespace writer {
+namespace spirv {
+namespace {
+
+using BuilderTest = testing::Test;
+
+TEST_F(BuilderTest, GlobalVar_NoStorageClass) {
+  ast::type::F32Type f32;
+  ast::Variable v("var", ast::StorageClass::kNone, &f32);
+
+  Builder b;
+  EXPECT_TRUE(b.GenerateGlobalVariable(&v)) << b.error();
+  EXPECT_EQ(DumpInstructions(b.debug()), R"(OpName %1 "var"
+)");
+  EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
+%2 = OpTypePointer Private %3
+%1 = OpVariable %2 Private
+)");
+}
+
+TEST_F(BuilderTest, GlobalVar_WithStorageClass) {
+  ast::type::F32Type f32;
+  ast::Variable v("var", ast::StorageClass::kOutput, &f32);
+
+  Builder b;
+  EXPECT_TRUE(b.GenerateGlobalVariable(&v)) << b.error();
+  EXPECT_EQ(DumpInstructions(b.debug()), R"(OpName %1 "var"
+)");
+  EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
+%2 = OpTypePointer Output %3
+%1 = OpVariable %2 Output
+)");
+}
+
+TEST_F(BuilderTest, DISABLED_GlobalVar_WithInitializer) {}
+
+TEST_F(BuilderTest, DISABLED_GlobalVar_Const) {}
+
+TEST_F(BuilderTest, GlobalVar_WithLocation) {
+  ast::type::F32Type f32;
+  auto v =
+      std::make_unique<ast::Variable>("var", ast::StorageClass::kOutput, &f32);
+  std::vector<std::unique_ptr<ast::VariableDecoration>> decos;
+  decos.push_back(std::make_unique<ast::LocationDecoration>(5));
+
+  ast::DecoratedVariable dv(std::move(v));
+  dv.set_decorations(std::move(decos));
+
+  Builder b;
+  EXPECT_TRUE(b.GenerateGlobalVariable(&dv)) << b.error();
+  EXPECT_EQ(DumpInstructions(b.debug()), R"(OpName %1 "var"
+OpDecorate %1 Location 5
+)");
+  EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
+%2 = OpTypePointer Output %3
+%1 = OpVariable %2 Output
+)");
+}
+
+TEST_F(BuilderTest, GlobalVar_WithBindingAndSet) {
+  ast::type::F32Type f32;
+  auto v =
+      std::make_unique<ast::Variable>("var", ast::StorageClass::kOutput, &f32);
+  std::vector<std::unique_ptr<ast::VariableDecoration>> decos;
+  decos.push_back(std::make_unique<ast::BindingDecoration>(2));
+  decos.push_back(std::make_unique<ast::SetDecoration>(3));
+
+  ast::DecoratedVariable dv(std::move(v));
+  dv.set_decorations(std::move(decos));
+
+  Builder b;
+  EXPECT_TRUE(b.GenerateGlobalVariable(&dv)) << b.error();
+  EXPECT_EQ(DumpInstructions(b.debug()), R"(OpName %1 "var"
+OpDecorate %1 Binding 2
+OpDecorate %1 DescriptorSet 3
+)");
+  EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
+%2 = OpTypePointer Output %3
+%1 = OpVariable %2 Output
+)");
+}
+
+TEST_F(BuilderTest, GlobalVar_WithBuiltin) {
+  ast::type::F32Type f32;
+  auto v =
+      std::make_unique<ast::Variable>("var", ast::StorageClass::kOutput, &f32);
+  std::vector<std::unique_ptr<ast::VariableDecoration>> decos;
+  decos.push_back(
+      std::make_unique<ast::BuiltinDecoration>(ast::Builtin::kPosition));
+
+  ast::DecoratedVariable dv(std::move(v));
+  dv.set_decorations(std::move(decos));
+
+  Builder b;
+  EXPECT_TRUE(b.GenerateGlobalVariable(&dv)) << b.error();
+  EXPECT_EQ(DumpInstructions(b.debug()), R"(OpName %1 "var"
+OpDecorate %1 BuiltIn Position
+)");
+  EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
+%2 = OpTypePointer Output %3
+%1 = OpVariable %2 Output
+)");
+}
+
+struct BuiltinData {
+  ast::Builtin builtin;
+  SpvBuiltIn result;
+};
+inline std::ostream& operator<<(std::ostream& out, BuiltinData data) {
+  out << data.builtin;
+  return out;
+}
+using BuiltinDataTest = testing::TestWithParam<BuiltinData>;
+TEST_P(BuiltinDataTest, Convert) {
+  auto params = GetParam();
+
+  Builder b;
+  EXPECT_EQ(b.ConvertBuiltin(params.builtin), params.result);
+}
+INSTANTIATE_TEST_SUITE_P(
+    BuilderTest_Type,
+    BuiltinDataTest,
+    testing::Values(
+        BuiltinData{ast::Builtin::kNone, SpvBuiltInMax},
+        BuiltinData{ast::Builtin::kPosition, SpvBuiltInPosition},
+        BuiltinData{
+            ast::Builtin::kVertexIdx,
+            SpvBuiltInVertexIndex,
+        },
+        BuiltinData{ast::Builtin::kInstanceIdx, SpvBuiltInInstanceIndex},
+        BuiltinData{ast::Builtin::kFrontFacing, SpvBuiltInFrontFacing},
+        BuiltinData{ast::Builtin::kFragCoord, SpvBuiltInFragCoord},
+        BuiltinData{ast::Builtin::kFragDepth, SpvBuiltInFragDepth},
+        BuiltinData{ast::Builtin::kNumWorkgroups, SpvBuiltInNumWorkgroups},
+        BuiltinData{ast::Builtin::kWorkgroupSize, SpvBuiltInWorkgroupSize},
+        BuiltinData{ast::Builtin::kLocalInvocationId,
+                    SpvBuiltInLocalInvocationId},
+        BuiltinData{ast::Builtin::kLocalInvocationIdx,
+                    SpvBuiltInLocalInvocationIndex},
+        BuiltinData{ast::Builtin::kGlobalInvocationId,
+                    SpvBuiltInGlobalInvocationId}));
+
+}  // namespace
+}  // namespace spirv
+}  // namespace writer
+}  // namespace tint