diff --git a/lib/_http_agent.js b/lib/_http_agent.js
index ddb1c5bfff9b63..2a449e3cd4f729 100644
--- a/lib/_http_agent.js
+++ b/lib/_http_agent.js
@@ -28,7 +28,7 @@ function Agent(options) {
   self.defaultPort = 80;
   self.protocol = 'http:';
 
-  self.options = util._extend({}, options);
+  self.options = Object.assign({}, options);
 
   // don't confuse net and make it think that we're connecting to a pipe
   self.options.path = null;
@@ -151,8 +151,7 @@ Agent.prototype.addRequest = function(req, options) {
 
 Agent.prototype.createSocket = function(req, options) {
   var self = this;
-  options = util._extend({}, options);
-  options = util._extend(options, self.options);
+  options = Object.assign({}, options, self.options);
 
   if (!options.servername) {
     options.servername = options.host;
diff --git a/lib/_http_client.js b/lib/_http_client.js
index 34072f8f996840..9791ff4a120a1e 100644
--- a/lib/_http_client.js
+++ b/lib/_http_client.js
@@ -25,7 +25,7 @@ function ClientRequest(options, cb) {
       throw new Error('Unable to determine the domain name');
     }
   } else {
-    options = util._extend({}, options);
+    options = Object.assign({}, options);
   }
 
   var agent = options.agent;
diff --git a/lib/_tls_wrap.js b/lib/_tls_wrap.js
index d3df48a4c59fc7..4e2d479bebf2f0 100644
--- a/lib/_tls_wrap.js
+++ b/lib/_tls_wrap.js
@@ -947,9 +947,9 @@ function normalizeConnectArgs(listArgs) {
   var cb = args[1];
 
   if (listArgs[1] !== null && typeof listArgs[1] === 'object') {
-    options = util._extend(options, listArgs[1]);
+    options = Object.assign(options, listArgs[1]);
   } else if (listArgs[2] !== null && typeof listArgs[2] === 'object') {
-    options = util._extend(options, listArgs[2]);
+    options = Object.assign(options, listArgs[2]);
   }
 
   return (cb) ? [options, cb] : [options];
@@ -967,7 +967,7 @@ exports.connect = function(/* [port, host], options, cb */) {
     minDHSize: 1024
   };
 
-  options = util._extend(defaults, options || {});
+  options = Object.assign(defaults, options);
   if (!options.keepAlive)
     options.singleUse = true;
 
diff --git a/lib/child_process.js b/lib/child_process.js
index ee73562d24e80f..708bd1e3a46268 100644
--- a/lib/child_process.js
+++ b/lib/child_process.js
@@ -22,12 +22,12 @@ exports.fork = function(modulePath /*, args, options*/) {
   var options, args, execArgv;
   if (Array.isArray(arguments[1])) {
     args = arguments[1];
-    options = util._extend({}, arguments[2]);
+    options = Object.assign({}, arguments[2]);
   } else if (arguments[1] && typeof arguments[1] !== 'object') {
     throw new TypeError('Incorrect value of args option');
   } else {
     args = [];
-    options = util._extend({}, arguments[1]);
+    options = Object.assign({}, arguments[1]);
   }
 
   // Prepare arguments for fork:
@@ -86,7 +86,7 @@ function normalizeExecArgs(command /*, options, callback*/) {
     args = ['/s', '/c', '"' + command + '"'];
     // Make a shallow copy before patching so we don't clobber the user's
     // options object.
-    options = util._extend({}, options);
+    options = Object.assign({}, options);
     options.windowsVerbatimArguments = true;
   } else {
     file = '/bin/sh';
@@ -135,7 +135,7 @@ exports.execFile = function(file /*, args, options, callback*/) {
   }
 
   if (pos < arguments.length && typeof arguments[pos] === 'object') {
-    options = util._extend(options, arguments[pos++]);
+    options = Object.assign(options, arguments[pos++]);
   } else if (pos < arguments.length && arguments[pos] == null) {
     pos++;
   }
@@ -331,7 +331,7 @@ function normalizeSpawnArguments(file /*, args, options*/) {
   else if (options === null || typeof options !== 'object')
     throw new TypeError('"options" argument must be an object');
 
-  options = util._extend({}, options);
+  options = Object.assign({}, options);
   args.unshift(file);
 
   var env = options.env || process.env;
@@ -405,7 +405,7 @@ function spawnSync(/*file, args, options*/) {
   options.stdio = _validateStdio(options.stdio || 'pipe', true).stdio;
 
   if (options.input) {
-    var stdin = options.stdio[0] = util._extend({}, options.stdio[0]);
+    var stdin = options.stdio[0] = Object.assign({}, options.stdio[0]);
     stdin.input = options.input;
   }
 
@@ -413,7 +413,7 @@ function spawnSync(/*file, args, options*/) {
   for (i = 0; i < options.stdio.length; i++) {
     var input = options.stdio[i] && options.stdio[i].input;
     if (input != null) {
-      var pipe = options.stdio[i] = util._extend({}, options.stdio[i]);
+      var pipe = options.stdio[i] = Object.assign({}, options.stdio[i]);
       if (Buffer.isBuffer(input))
         pipe.input = input;
       else if (typeof input === 'string')
@@ -445,7 +445,7 @@ function spawnSync(/*file, args, options*/) {
     result.error.spawnargs = opts.args.slice(1);
   }
 
-  util._extend(result, opts);
+  Object.assign(result, opts);
 
   return result;
 }
@@ -464,7 +464,7 @@ function checkExecSyncError(ret) {
       err = new Error(msg);
     }
 
-    util._extend(err, ret);
+    Object.assign(err, ret);
     return err;
   }
 
diff --git a/lib/cluster.js b/lib/cluster.js
index 8356fad88a60d0..6f148ac5426a85 100644
--- a/lib/cluster.js
+++ b/lib/cluster.js
@@ -231,8 +231,7 @@ function masterInit() {
       execArgv: process.execArgv,
       silent: false
     };
-    settings = util._extend(settings, cluster.settings);
-    settings = util._extend(settings, options || {});
+    settings = Object.assign(settings, cluster.settings, options);
     // Tell V8 to write profile data for each process to a separate file.
     // Without --logfile=v8-%p.log, everything ends up in a single, unusable
     // file. (Unusable because what V8 logs are memory addresses and each
@@ -285,10 +284,9 @@ function masterInit() {
   var debugPortOffset = 1;
 
   function createWorkerProcess(id, env) {
-    var workerEnv = util._extend({}, process.env);
+    var workerEnv = Object.assign({}, process.env, env);
     var execArgv = cluster.settings.execArgv.slice();
 
-    workerEnv = util._extend(workerEnv, env);
     workerEnv.NODE_UNIQUE_ID = '' + id;
 
     for (var i = 0; i < execArgv.length; i++) {
@@ -478,7 +476,7 @@ function masterInit() {
 
     // Set custom server data
     handle.add(worker, function(errno, reply, handle) {
-      reply = util._extend({
+      reply = Object.assign({
         errno: errno,
         key: key,
         ack: message.seq,
@@ -556,7 +554,7 @@ function workerInit() {
     else
       indexes[key]++;
 
-    const message = util._extend({
+    const message = Object.assign({
       act: 'queryServer',
       index: indexes[key],
       data: null
@@ -623,7 +621,7 @@ function workerInit() {
     }
 
     function getsockname(out) {
-      if (key) util._extend(out, message.sockname);
+      if (key) Object.assign(out, message.sockname);
       return 0;
     }
 
@@ -702,7 +700,7 @@ var seq = 0;
 var callbacks = {};
 function sendHelper(proc, message, handle, cb) {
   // Mark message as internal. See INTERNAL_PREFIX in lib/child_process.js
-  message = util._extend({ cmd: 'NODE_CLUSTER' }, message);
+  message = Object.assign({ cmd: 'NODE_CLUSTER' }, message);
   if (cb) callbacks[seq] = cb;
   message.seq = seq;
   seq += 1;
diff --git a/lib/console.js b/lib/console.js
index a0eec4e34878be..c91c770fc6240f 100644
--- a/lib/console.js
+++ b/lib/console.js
@@ -49,7 +49,7 @@ Console.prototype.error = Console.prototype.warn;
 
 
 Console.prototype.dir = function(object, options) {
-  this._stdout.write(util.inspect(object, util._extend({
+  this._stdout.write(util.inspect(object, Object.assign({
     customInspect: false
   }, options)) + '\n');
 };
diff --git a/lib/domain.js b/lib/domain.js
index 630d02ec332751..6c250731dcee8a 100644
--- a/lib/domain.js
+++ b/lib/domain.js
@@ -239,7 +239,7 @@ function intercepted(_this, self, cb, fnargs) {
 
   if (fnargs[0] && fnargs[0] instanceof Error) {
     var er = fnargs[0];
-    util._extend(er, {
+    Object.assign(er, {
       domainBound: cb,
       domainThrown: false,
       domain: self
diff --git a/lib/fs.js b/lib/fs.js
index 54e6b4ac0d2536..995162e47b1a3e 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -1269,7 +1269,7 @@ fs.appendFile = function(path, data, options, callback_) {
   }
 
   if (!options.flag)
-    options = util._extend({ flag: 'a' }, options);
+    options = Object.assign({ flag: 'a' }, options);
 
   // force append behavior when using a supplied file descriptor
   if (isFd(path))
@@ -1288,7 +1288,7 @@ fs.appendFileSync = function(path, data, options) {
   }
 
   if (!options.flag)
-    options = util._extend({ flag: 'a' }, options);
+    options = Object.assign({ flag: 'a' }, options);
 
   // force append behavior when using a supplied file descriptor
   if (isFd(path))
@@ -1417,7 +1417,7 @@ fs.watchFile = function(filename, options, listener) {
   };
 
   if (options !== null && typeof options === 'object') {
-    options = util._extend(defaults, options);
+    options = Object.assign(defaults, options);
   } else {
     listener = options;
     options = defaults;
diff --git a/lib/https.js b/lib/https.js
index 7008a79131c663..4c5bdc925cf8de 100644
--- a/lib/https.js
+++ b/lib/https.js
@@ -71,7 +71,7 @@ function createConnection(port, host, options) {
     const session = this._getSession(options._agentKey);
     if (session) {
       debug('reuse session for %j', options._agentKey);
-      options = util._extend({
+      options = Object.assign({
         session: session
       }, options);
     }
@@ -176,7 +176,7 @@ exports.request = function(options, cb) {
       throw new Error('Unable to determine the domain name');
     }
   } else {
-    options = util._extend({}, options);
+    options = Object.assign({}, options);
   }
   options._defaultAgent = globalAgent;
   return http.request(options, cb);
diff --git a/lib/tty.js b/lib/tty.js
index 72efcd078b2892..90d13f7bb36f0d 100644
--- a/lib/tty.js
+++ b/lib/tty.js
@@ -17,7 +17,7 @@ function ReadStream(fd, options) {
   if (!(this instanceof ReadStream))
     return new ReadStream(fd, options);
 
-  options = util._extend({
+  options = Object.assign({
     highWaterMark: 0,
     readable: true,
     writable: false,
diff --git a/lib/util.js b/lib/util.js
index 50cc5bc5b4b25d..d38fdbc593746f 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -98,7 +98,7 @@ function inspect(obj, opts) {
     ctx.showHidden = opts;
   } else if (opts) {
     // got an "options" object
-    exports._extend(ctx, opts);
+    Object.assign(ctx, opts);
   }
   // set default options
   if (ctx.showHidden === undefined) ctx.showHidden = false;
@@ -806,7 +806,14 @@ exports.inherits = function(ctor, superCtor) {
   Object.setPrototypeOf(ctor.prototype, superCtor.prototype);
 };
 
-exports._extend = function(origin, add) {
+function hasOwnProperty(obj, prop) {
+  return Object.prototype.hasOwnProperty.call(obj, prop);
+}
+
+
+// Deprecated old stuff.
+
+exports._extend = internalUtil.deprecate(function(origin, add) {
   // Don't do anything if add isn't an object
   if (add === null || typeof add !== 'object') return origin;
 
@@ -816,14 +823,7 @@ exports._extend = function(origin, add) {
     origin[keys[i]] = add[keys[i]];
   }
   return origin;
-};
-
-function hasOwnProperty(obj, prop) {
-  return Object.prototype.hasOwnProperty.call(obj, prop);
-}
-
-
-// Deprecated old stuff.
+}, 'util._extend is deprecated. Use Object.assign or a module instead.');
 
 exports.print = internalUtil.deprecate(function() {
   for (var i = 0, len = arguments.length; i < len; ++i) {
diff --git a/test/parallel/test-crypto.js b/test/parallel/test-crypto.js
index df59fd9bded726..725ada4cfad5cd 100644
--- a/test/parallel/test-crypto.js
+++ b/test/parallel/test-crypto.js
@@ -1,7 +1,6 @@
 'use strict';
 var common = require('../common');
 var assert = require('assert');
-var util = require('util');
 
 if (!common.hasCrypto) {
   console.log('1..0 # Skipped: missing crypto');
@@ -56,7 +55,7 @@ assert.throws(function() {
 
 function assertSorted(list) {
   // Array#sort() modifies the list in place so make a copy.
-  var sorted = util._extend([], list).sort();
+  var sorted = Object.assign([], list).sort();
   assert.deepEqual(list, sorted);
 }
 
diff --git a/test/parallel/test-http-methods.js b/test/parallel/test-http-methods.js
index 62a4187841bdbc..64d01421c75fdf 100644
--- a/test/parallel/test-http-methods.js
+++ b/test/parallel/test-http-methods.js
@@ -2,11 +2,10 @@
 require('../common');
 var assert = require('assert');
 var http = require('http');
-var util = require('util');
 
 assert(Array.isArray(http.METHODS));
 assert(http.METHODS.length > 0);
 assert(http.METHODS.indexOf('GET') !== -1);
 assert(http.METHODS.indexOf('HEAD') !== -1);
 assert(http.METHODS.indexOf('POST') !== -1);
-assert.deepEqual(util._extend([], http.METHODS), http.METHODS.sort());
+assert.deepEqual(Object.assign([], http.METHODS), http.METHODS.sort());
diff --git a/test/parallel/test-http-server-stale-close.js b/test/parallel/test-http-server-stale-close.js
index 349e869c1a4fbc..43b196d52796b1 100644
--- a/test/parallel/test-http-server-stale-close.js
+++ b/test/parallel/test-http-server-stale-close.js
@@ -1,7 +1,6 @@
 'use strict';
 var common = require('../common');
 var http = require('http');
-var util = require('util');
 var fork = require('child_process').fork;
 
 if (process.env.NODE_TEST_FORK) {
@@ -25,7 +24,7 @@ else {
   });
   server.listen(common.PORT, function() {
     fork(__filename, {
-      env: util._extend(process.env, {NODE_TEST_FORK: '1'})
+      env: Object.assign(process.env, {NODE_TEST_FORK: '1'})
     });
   });
 }
diff --git a/test/parallel/test-readline-keys.js b/test/parallel/test-readline-keys.js
index e026c0b583cd9e..6e720e7e833313 100644
--- a/test/parallel/test-readline-keys.js
+++ b/test/parallel/test-readline-keys.js
@@ -3,7 +3,6 @@ require('../common');
 var PassThrough = require('stream').PassThrough;
 var assert = require('assert');
 var inherits = require('util').inherits;
-var extend = require('util')._extend;
 var Interface = require('readline').Interface;
 
 
@@ -33,7 +32,7 @@ function addTest(sequences, expectedKeys) {
   }
 
   expectedKeys = expectedKeys.map(function(k) {
-    return k ? extend({ ctrl: false, meta: false, shift: false }, k) : k;
+    return k ? Object.assign({ ctrl: false, meta: false, shift: false }, k) : k;
   });
 
   keys = [];
diff --git a/test/parallel/test-util.js b/test/parallel/test-util.js
index 864361d80a6dfa..3f10b934e27485 100644
--- a/test/parallel/test-util.js
+++ b/test/parallel/test-util.js
@@ -74,12 +74,3 @@ assert.equal(true, util.isPrimitive(Symbol('symbol')));
 // isBuffer
 assert.equal(false, util.isBuffer('foo'));
 assert.equal(true, util.isBuffer(new Buffer('foo')));
-
-// _extend
-assert.deepEqual(util._extend({a:1}),             {a:1});
-assert.deepEqual(util._extend({a:1}, []),         {a:1});
-assert.deepEqual(util._extend({a:1}, null),       {a:1});
-assert.deepEqual(util._extend({a:1}, true),       {a:1});
-assert.deepEqual(util._extend({a:1}, false),      {a:1});
-assert.deepEqual(util._extend({a:1}, {b:2}),      {a:1, b:2});
-assert.deepEqual(util._extend({a:1, b:2}, {b:3}), {a:1, b:3});