Index: clang-tidy/ClangTidyOptions.h
===================================================================
--- clang-tidy/ClangTidyOptions.h
+++ clang-tidy/ClangTidyOptions.h
@@ -87,6 +87,10 @@
   /// \brief Key-value mapping used to store check-specific options.
   OptionMap CheckOptions;
 
+  /// \brief Key-value mapping used to store relationship between check filters
+  /// and the source file where the filters come from.
+  OptionMap CheckSources;
+
   typedef std::vector<std::string> ArgList;
 
   /// \brief Add extra compilation arguments to the end of the list.
Index: clang-tidy/ClangTidyOptions.cpp
===================================================================
--- clang-tidy/ClangTidyOptions.cpp
+++ clang-tidy/ClangTidyOptions.cpp
@@ -121,10 +121,14 @@
   ClangTidyOptions Result = *this;
 
   // Merge comma-separated glob lists by appending the new value after a comma.
-  if (Other.Checks)
+  if (Other.Checks) {
     Result.Checks =
         (Result.Checks && !Result.Checks->empty() ? *Result.Checks + "," : "") +
         *Other.Checks;
+    const auto it = Other.CheckSources.find(*Other.Checks);
+    if (it != Other.CheckSources.end())
+      Result.CheckSources[*Other.Checks] = it->second;
+  }
   if (Other.WarningsAsErrors)
     Result.WarningsAsErrors =
         (Result.WarningsAsErrors && !Result.WarningsAsErrors->empty()
@@ -255,7 +259,10 @@
                      << ParsedOptions.getError().message() << "\n";
       continue;
     }
-
+    if (ParsedOptions->Checks) {
+      ParsedOptions->CheckSources[*ParsedOptions->Checks] =
+          std::string(ConfigFile.c_str());
+    }
     return DefaultOptionsProvider::getOptions(Directory)
         .mergeWith(*ParsedOptions)
         .mergeWith(OverrideOptions);
Index: clang-tidy/tool/ClangTidyMain.cpp
===================================================================
--- clang-tidy/tool/ClangTidyMain.cpp
+++ clang-tidy/tool/ClangTidyMain.cpp
@@ -128,6 +128,12 @@
 )"),
                                 cl::init(false), cl::cat(ClangTidyCategory));
 
+static cl::opt<bool> ExplainChecks("explain-checks", cl::desc(R"(
+explains where each check comes from, i.e. command line, .clang-tidy
+configuration file.
+)"),
+                                   cl::init(false), cl::cat(ClangTidyCategory));
+
 static cl::opt<std::string> Config("config", cl::desc(R"(
 Specifies a configuration in YAML/JSON format:
   -config="{Checks: '*',
@@ -256,6 +262,7 @@
 
   ClangTidyOptions DefaultOptions;
   DefaultOptions.Checks = DefaultChecks;
+  DefaultOptions.CheckSources[DefaultChecks] = "ClangTidy binary";
   DefaultOptions.WarningsAsErrors = "";
   DefaultOptions.HeaderFilterRegex = HeaderFilter;
   DefaultOptions.SystemHeaders = SystemHeaders;
@@ -266,8 +273,10 @@
     DefaultOptions.User = llvm::sys::Process::GetEnv("USERNAME");
 
   ClangTidyOptions OverrideOptions;
-  if (Checks.getNumOccurrences() > 0)
+  if (Checks.getNumOccurrences() > 0) {
     OverrideOptions.Checks = Checks;
+    OverrideOptions.CheckSources[Checks] = "command-line argument 'checks'";
+  }
   if (WarningsAsErrors.getNumOccurrences() > 0)
     OverrideOptions.WarningsAsErrors = WarningsAsErrors;
   if (HeaderFilter.getNumOccurrences() > 0)
@@ -280,6 +289,10 @@
   if (!Config.empty()) {
     if (llvm::ErrorOr<ClangTidyOptions> ParsedConfig =
             parseConfiguration(Config)) {
+      if (ParsedConfig->Checks) {
+        ParsedConfig->CheckSources[*ParsedConfig->Checks] =
+            "command-line argument 'config'";
+      }
       return llvm::make_unique<DefaultOptionsProvider>(
           GlobalOptions, ClangTidyOptions::getDefaults()
                              .mergeWith(DefaultOptions)
@@ -311,6 +324,20 @@
   ClangTidyOptions EffectiveOptions = OptionsProvider->getOptions(FileName);
   std::vector<std::string> EnabledChecks = getCheckNames(EffectiveOptions);
 
+  if (ExplainChecks) {
+    for (const std::string& Check : EnabledChecks) {
+      for (const ClangTidyOptions::StringPair &CheckSource:
+           EffectiveOptions.CheckSources) {
+        GlobList filter(CheckSource.first);
+        if (filter.contains(Check)) {
+          llvm::outs() << "'" << Check << "' comes from " << CheckSource.second
+                       << ".\n";
+        }
+      }
+    }
+    return 0;
+  }
+
   if (ListChecks) {
     llvm::outs() << "Enabled checks:";
     for (auto CheckName : EnabledChecks)
Index: test/clang-tidy/Inputs/explain-checks/.clang-tidy
===================================================================
--- /dev/null
+++ test/clang-tidy/Inputs/explain-checks/.clang-tidy
@@ -0,0 +1 @@
+Checks: '-*,modernize-use-nullptr'
Index: test/clang-tidy/explain-checks.cpp
===================================================================
--- /dev/null
+++ test/clang-tidy/explain-checks.cpp
@@ -0,0 +1,11 @@
+// RUN: clang-tidy -checks=-*,modernize-use-nullptr -explain-checks | FileCheck --check-prefix=CHECK-MESSAGE1 %s
+// RUN: clang-tidy -config="{Checks: '-*,modernize-use-nullptr'}" -explain-checks | FileCheck --check-prefix=CHECK-MESSAGE2 %s
+// RUN: clang-tidy -checks=modernize-use-nullptr -config="{Checks: '-*,modernize-use-nullptr'}" -explain-checks | FileCheck --check-prefix=CHECK-MESSAGE3 %s
+// RUN: clang-tidy -explain-checks | grep "'.*' comes from ClangTidy binary"
+// RUN: clang-tidy -explain-checks %S/Inputs/explain-checks/a.cc | grep "'modernize-use-nullptr' comes from %S/Inputs/explain-checks/.clang-tidy."
+
+// CHECK-MESSAGE1: 'modernize-use-nullptr' comes from command-line argument 'checks'.
+// CHECK-MESSAGE2: 'modernize-use-nullptr' comes from command-line argument 'config'.
+
+// CHECK-MESSAGE3: 'modernize-use-nullptr' comes from command-line argument 'config'.
+// CHECK-MESSAGE3: 'modernize-use-nullptr' comes from command-line argument 'checks'.