diff --git a/lld/MachO/CMakeLists.txt b/lld/MachO/CMakeLists.txt
--- a/lld/MachO/CMakeLists.txt
+++ b/lld/MachO/CMakeLists.txt
@@ -23,6 +23,7 @@
   Symbols.cpp
   SyntheticSections.cpp
   Target.cpp
+  MapFile.cpp
   Writer.cpp
 
   LINK_COMPONENTS
diff --git a/lld/MachO/Config.h b/lld/MachO/Config.h
--- a/lld/MachO/Config.h
+++ b/lld/MachO/Config.h
@@ -84,6 +84,7 @@
   uint32_t dylibCompatibilityVersion = 0;
   uint32_t dylibCurrentVersion = 0;
   llvm::StringRef installName;
+  llvm::StringRef mapFile;
   llvm::StringRef outputFile;
   llvm::StringRef ltoObjPath;
   bool demangle = false;
diff --git a/lld/MachO/Driver.cpp b/lld/MachO/Driver.cpp
--- a/lld/MachO/Driver.cpp
+++ b/lld/MachO/Driver.cpp
@@ -827,6 +827,7 @@
   for (auto *arg : args.filtered(OPT_U))
     symtab->addDynamicLookup(arg->getValue());
 
+  config->mapFile = args.getLastArgValue(OPT_map);
   config->outputFile = args.getLastArgValue(OPT_o, "a.out");
   config->installName =
       args.getLastArgValue(OPT_install_name, config->outputFile);
diff --git a/lld/MachO/MapFile.h b/lld/MachO/MapFile.h
new file mode 100644
--- /dev/null
+++ b/lld/MachO/MapFile.h
@@ -0,0 +1,18 @@
+//===- MapFile.h ------------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_MACHO_MAPFILE_H
+#define LLD_MACHO_MAPFILE_H
+
+namespace lld {
+namespace macho {
+void writeMapFile();
+} // namespace macho
+} // namespace lld
+
+#endif
diff --git a/lld/MachO/MapFile.cpp b/lld/MachO/MapFile.cpp
new file mode 100644
--- /dev/null
+++ b/lld/MachO/MapFile.cpp
@@ -0,0 +1,153 @@
+//===- MapFile.cpp --------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the -Map option. It shows lists in order and
+// hierarchically the outputFile, arch, input files, output sections and
+// symbol:
+//
+// # Path: test
+// # Arch: x86_84
+// # Object files:
+// [  0] linker synthesized
+// [  1] a.o
+// # Sections:
+// # Address  Size      Segment  Section
+// 0x1000005C0  0x0000004C  __TEXT  __text
+// # Symbols:
+// # Address  File  Name
+// 0x1000005C0  [  1] _main
+//
+//===----------------------------------------------------------------------===//
+
+#include "MapFile.h"
+#include "Config.h"
+#include "InputFiles.h"
+#include "InputSection.h"
+#include "OutputSection.h"
+#include "OutputSegment.h"
+#include "Symbols.h"
+#include "Target.h"
+
+using namespace llvm;
+using namespace llvm::MachO;
+using namespace llvm::sys;
+using namespace lld;
+using namespace lld::macho;
+
+using SymbolMapTy = DenseMap<const InputSection *, SmallVector<Defined *, 4>>;
+
+// Returns a map from sections to their symbols.
+static SymbolMapTy getSectionSyms(ArrayRef<Defined *> syms) {
+  SymbolMapTy ret;
+  for (Defined *dr : syms)
+    ret[dr->isec].push_back(dr);
+
+  // Sort symbols by address. We want to print out symbols in the
+  // order in the output file rather than the order they appeared
+  // in the input files.
+  for (auto &it : ret)
+    llvm::stable_sort(it.second, [](Defined *a, Defined *b) {
+      return a->getVA() < b->getVA();
+    });
+  return ret;
+}
+
+// Returns a list of all symbols that we want to print out.
+static std::vector<Defined *> getSymbols() {
+  std::vector<Defined *> v;
+  for (InputFile *file : inputFiles)
+    if (isa<ObjFile>(file))
+      for (lld::macho::Symbol *sym : file->symbols)
+        if (auto *d = dyn_cast<Defined>(sym))
+          if (d->isec && d->getFile() == file)
+            v.push_back(d);
+  return v;
+}
+
+// Construct a map from symbols to their stringified representations.
+// Demangling symbols (which is what toString() does) is slow, so
+// we do that in batch using parallel-for.
+static DenseMap<macho::Symbol *, std::string>
+getSymbolStrings(ArrayRef<Defined *> syms) {
+  std::vector<std::string> str(syms.size());
+  DenseMap<macho::Symbol *, std::string> ret;
+  for (size_t i = 0, e = syms.size(); i < e; ++i)
+    ret[syms[i]] = toString(*syms[i]);
+  return ret;
+}
+
+static llvm::StringRef getArchName(Architecture Arch) {
+  switch (Arch) {
+  case AK_x86_64:
+    return "x86_84";
+  case AK_arm64:
+    return "arm64";
+  default:
+    fatal("missing or unsupported arch");
+  }
+}
+
+void macho::writeMapFile() {
+  if (config->mapFile.empty())
+    return;
+
+  // Open a map file for writing.
+  std::error_code ec;
+  raw_fd_ostream os(config->mapFile, ec, sys::fs::OF_None);
+  if (ec) {
+    error("cannot open " + config->mapFile + ": " + ec.message());
+    return;
+  }
+
+  // Dump output path
+  os << format("# Path: %s\n", config->outputFile.str().c_str());
+
+  // Dump output architecure
+  os << format("# Arch: %s\n", getArchName(config->target.Arch).str().c_str());
+
+  // Dump table of object files
+  os << "# Object files:\n";
+  os << format("[%3u] %s\n", 0, (const char *)"linker synthesized");
+  uint32_t fileIndex = 1;
+  DenseMap<lld::macho::InputFile *, uint32_t> readerToFileOrdinal;
+  for (InputFile *file : inputFiles) {
+    if (isa<ObjFile>(file)) {
+      os << format("[%3u] %s\n", fileIndex, file->getName().str().c_str());
+      readerToFileOrdinal[file] = fileIndex++;
+    }
+  }
+
+  // Collect symbol info that we want to print out.
+  std::vector<Defined *> syms = getSymbols();
+  SymbolMapTy sectionSyms = getSectionSyms(syms);
+  DenseMap<lld::macho::Symbol *, std::string> symStr = getSymbolStrings(syms);
+
+  // Dump table of sections
+  os << "# Sections:\n";
+  os << "# Address\tSize    \tSegment\tSection\n";
+  for (OutputSegment *seg : outputSegments)
+    for (OutputSection *osec : seg->getSections()) {
+      if (osec->isHidden())
+        continue;
+
+      os << format("0x%08llX\t0x%08llX\t%s\t%s\n", osec->addr, osec->getSize(),
+                   seg->name.str().c_str(), osec->name.str().c_str());
+    }
+
+  // Dump table of symbols
+  os << "# Symbols:\n";
+  os << "# Address\t    File  Name\n";
+  for (InputSection *isec : inputSections) {
+    for (macho::Symbol *sym : sectionSyms[isec]) {
+      os << format("0x%08llX\t[%3u] %s\n", sym->getVA(),
+                   readerToFileOrdinal[sym->getFile()], symStr[sym].c_str());
+    }
+  }
+
+  // TODO: when we implement -dead_strip, we should dump dead stripped symbols
+}
diff --git a/lld/MachO/Writer.cpp b/lld/MachO/Writer.cpp
--- a/lld/MachO/Writer.cpp
+++ b/lld/MachO/Writer.cpp
@@ -10,6 +10,7 @@
 #include "Config.h"
 #include "InputFiles.h"
 #include "InputSection.h"
+#include "MapFile.h"
 #include "MergedOutputSection.h"
 #include "OutputSection.h"
 #include "OutputSegment.h"
@@ -886,6 +887,8 @@
   // addresses and offsets.
   assignAddresses(linkEditSegment);
 
+  writeMapFile();
+
   openFile();
   if (errorCount())
     return;