Index: clang-tidy/google/AssignOperatorSignatureCheck.h
===================================================================
--- /dev/null
+++ clang-tidy/google/AssignOperatorSignatureCheck.h
@@ -0,0 +1,35 @@
+//===--- AssignOperatorSignatureCheck.h - clang-tidy ------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_GOOGLE_ASSIGN_OPERATOR_SIGNATURE_CHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_GOOGLE_ASSIGN_OPERATOR_SIGNATURE_CHECK_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace readability {
+
+/// \brief Finds declarations of assign operators with the wrong return type.
+///
+/// The return type must be \c Class&.
+/// Works with move-assign. Private and deleted operators are ignored.
+class AssignOperatorSignatureCheck : public ClangTidyCheck {
+public:
+  AssignOperatorSignatureCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace readability
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_GOOGLE_ASSIGN_OPERATOR_SIGNATURE_CHECK_H
Index: clang-tidy/google/AssignOperatorSignatureCheck.cpp
===================================================================
--- /dev/null
+++ clang-tidy/google/AssignOperatorSignatureCheck.cpp
@@ -0,0 +1,69 @@
+//===--- AssignOperatorSignatureCheck.cpp - clang-tidy ----------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "AssignOperatorSignatureCheck.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace readability {
+
+void AssignOperatorSignatureCheck::registerMatchers(
+    ast_matchers::MatchFinder *Finder) {
+  const auto HasGoodReturnType = methodDecl(returns(lValueReferenceType(pointee(
+      unless(isConstQualified()), hasDeclaration(equalsBoundNode("class"))))));
+
+  const auto IsSelf = qualType(
+      anyOf(hasDeclaration(equalsBoundNode("class")),
+            referenceType(pointee(hasDeclaration(equalsBoundNode("class"))))));
+  const auto IsSelfAssign =
+      methodDecl(unless(anyOf(isDeleted(), isPrivate())), hasName("operator="),
+                 ofClass(recordDecl().bind("class")),
+                 hasParameter(0, parmVarDecl(hasType(IsSelf)))).bind("method");
+
+  Finder->addMatcher(
+      methodDecl(IsSelfAssign, unless(HasGoodReturnType)).bind("ReturnType"),
+      this);
+
+  const auto BadSelf = referenceType(
+      anyOf(lValueReferenceType(pointee(unless(isConstQualified()))),
+            rValueReferenceType(pointee(isConstQualified()))));
+
+  Finder->addMatcher(
+      methodDecl(IsSelfAssign, hasParameter(0, parmVarDecl(hasType(BadSelf))))
+          .bind("ArgumentType"),
+      this);
+
+  Finder->addMatcher(methodDecl(IsSelfAssign, isConst()).bind("Const"), this);
+}
+
+
+void AssignOperatorSignatureCheck::check(
+    const MatchFinder::MatchResult &Result) {
+  const auto* Method = Result.Nodes.getNodeAs<CXXMethodDecl>("method");
+  std::string Name = Method->getParent()->getName();
+
+  static const char *Messages[][2] = {
+      {"ReturnType", "operator=() should return '%0&'"},
+      {"ArgumentType", "operator=() should take '%0 const&', '%0&&' or '%0'"},
+      {"Const", "operator=() should not be marked 'const'"},
+  };
+
+  for (const auto& Message : Messages) {
+    if (Result.Nodes.getNodeAs<Decl>(Message[0]))
+      diag(Method->getLocStart(), Message[1]) << Name;
+  }
+}
+
+} // namespace readability
+} // namespace tidy
+} // namespace clang
Index: clang-tidy/google/CMakeLists.txt
===================================================================
--- clang-tidy/google/CMakeLists.txt
+++ clang-tidy/google/CMakeLists.txt
@@ -1,6 +1,7 @@
 set(LLVM_LINK_COMPONENTS support)
 
 add_clang_library(clangTidyGoogleModule
+  AssignOperatorSignatureCheck.cpp
   AvoidCStyleCastsCheck.cpp
   ExplicitConstructorCheck.cpp
   ExplicitMakePairCheck.cpp
Index: clang-tidy/google/GoogleTidyModule.cpp
===================================================================
--- clang-tidy/google/GoogleTidyModule.cpp
+++ clang-tidy/google/GoogleTidyModule.cpp
@@ -10,6 +10,7 @@
 #include "../ClangTidy.h"
 #include "../ClangTidyModule.h"
 #include "../ClangTidyModuleRegistry.h"
+#include "AssignOperatorSignatureCheck.h"
 #include "AvoidCStyleCastsCheck.h"
 #include "ExplicitConstructorCheck.h"
 #include "ExplicitMakePairCheck.h"
@@ -50,6 +51,8 @@
         "google-runtime-member-string-references");
     CheckFactories.registerCheck<runtime::MemsetZeroLengthCheck>(
         "google-runtime-memset");
+    CheckFactories.registerCheck<readability::AssignOperatorSignatureCheck>(
+        "google-readability-assign-operator");
     CheckFactories.registerCheck<readability::AvoidCStyleCastsCheck>(
         "google-readability-casting");
     CheckFactories.registerCheck<readability::NamedParameterCheck>(
Index: test/clang-tidy/google-assign-operator.cpp
===================================================================
--- /dev/null
+++ test/clang-tidy/google-assign-operator.cpp
@@ -0,0 +1,52 @@
+// RUN: $(dirname %s)/check_clang_tidy.sh %s google-readability-assign-operator %t
+// REQUIRES: shell
+
+struct Good {
+  Good& operator=(const Good&);
+  Good& operator=(Good&&);
+
+  // Assign from other types is fine too.
+  Good& operator=(int);
+};
+
+struct AlsoGood {
+  // By value is also fine.
+  AlsoGood& operator=(AlsoGood);
+};
+
+struct BadReturn {
+  void operator=(const BadReturn&);
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: operator=() should return 'BadReturn&' [google-readability-assign-operator]
+  const BadReturn& operator=(BadReturn&&);
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: operator=() should return 'Bad
+};
+struct BadReturn2 {
+  BadReturn2&& operator=(const BadReturn2&);
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: operator=() should return 'Bad
+  int operator=(BadReturn2&&);
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: operator=() should return 'Bad
+};
+
+struct BadArgument {
+  BadArgument& operator=(BadArgument&);
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: operator=() should take 'BadArgument const&', 'BadArgument&&' or 'BadArgument'
+  BadArgument& operator=(const BadArgument&&);
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: operator=() should take 'BadAr
+};
+
+struct BadModifier {
+  BadModifier& operator=(const BadModifier&) const;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: operator=() should not be marked 'const'
+};
+
+struct Deleted {
+  // We don't check the return value of deleted operators.
+  void operator=(const Deleted&) = delete;
+  void operator=(Deleted&&) = delete;
+};
+
+class Private {
+  // We don't check the return value of private operators.
+  // Pre-C++11 way of disabling assignment.
+  void operator=(const Private &);
+};