diff --git a/.gitignore b/.gitignore
index 8a7c4c92..da4200be 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,4 @@
-node_modules
+/node_modules
 npm-debug.log
 /errors
 /test.js
diff --git a/bin/prettier.js b/bin/prettier.js
index 36ca4907..1ba6baf3 100755
--- a/bin/prettier.js
+++ b/bin/prettier.js
@@ -3,6 +3,7 @@
 "use strict";
 
 const fs = require("fs");
+const path = require("path");
 const getStdin = require("get-stdin");
 const glob = require("glob");
 const chalk = require("chalk");
@@ -30,6 +31,7 @@ const argv = minimist(process.argv.slice(2), {
     "version",
     "debug-print-doc",
     "debug-check",
+    "with-node-modules",
     // Deprecated in 0.0.10
     "flow-parser"
   ],
@@ -64,6 +66,10 @@ if (argv["version"]) {
 const filepatterns = argv["_"];
 const write = argv["write"];
 const stdin = argv["stdin"] || (!filepatterns.length && !process.stdin.isTTY);
+const ignoreNodeModules = argv["with-node-modules"] === false;
+const globOptions = {
+  ignore: ignoreNodeModules && "**/node_modules/**"
+};
 
 if (write && argv["debug-check"]) {
   console.error("Cannot use --write and --debug-check together.");
@@ -341,11 +347,14 @@ if (stdin) {
 function eachFilename(patterns, callback) {
   patterns.forEach(pattern => {
     if (!glob.hasMagic(pattern)) {
+      if (shouldIgnorePattern(pattern)) {
+        return;
+      }
       callback(pattern);
       return;
     }
 
-    glob(pattern, (err, filenames) => {
+    glob(pattern, globOptions, (err, filenames) => {
       if (err) {
         console.error("Unable to expand glob pattern: " + pattern + "\n" + err);
         // Don't exit the process if one pattern failed
@@ -359,3 +368,7 @@ function eachFilename(patterns, callback) {
     });
   });
 }
+
+function shouldIgnorePattern(pattern) {
+  return ignoreNodeModules && path.resolve(pattern).includes("/node_modules/");
+}
diff --git a/package.json b/package.json
index b440fc7a..2ba129ba 100644
--- a/package.json
+++ b/package.json
@@ -22,6 +22,7 @@
     "minimist": "1.2.0"
   },
   "devDependencies": {
+    "cross-spawn": "^5.1.0",
     "diff": "3.2.0",
     "eslint": "^3.19.0",
     "eslint-plugin-prettier": "^2.1.1",
@@ -40,6 +41,7 @@
   },
   "scripts": {
     "test": "jest",
+    "test-integration": "jest tests_integration",
     "lint": "eslint .",
     "build:docs": "rollup -c docs/rollup.config.js"
   },
@@ -50,11 +52,10 @@
     "snapshotSerializers": [
       "<rootDir>/tests_config/raw-serializer.js"
     ],
-    "testRegex": "jsfmt\\.spec\\.js$",
+    "testRegex": "jsfmt\\.spec\\.js$|__tests__/.*\\.js$",
     "testPathIgnorePatterns": [
       "tests/new_react",
       "tests/more_react",
-
       "see https://github.com/eslint/typescript-eslint-parser/issues/269",
       "tests/typescript/conformance/types/abstractKeyword/jsfmt.spec.js"
     ]
diff --git a/tests_integration/.eslintrc.js b/tests_integration/.eslintrc.js
new file mode 100644
index 00000000..5c29e440
--- /dev/null
+++ b/tests_integration/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  env: {
+    jest: true
+  }
+};
diff --git a/tests_integration/__tests__/__snapshots__/with-node-modules.js.snap b/tests_integration/__tests__/__snapshots__/with-node-modules.js.snap
new file mode 100644
index 00000000..5fb7217a
--- /dev/null
+++ b/tests_integration/__tests__/__snapshots__/with-node-modules.js.snap
@@ -0,0 +1,27 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`doesn't ignore node_modules with --with-node-modules flag 1`] = `
+"node_modules/node-module.js
+not_node_modules/file.js
+regular-module.js
+"
+`;
+
+exports[`doesn't ignore node_modules with --with-node-modules flag for file list 1`] = `
+"node_modules/node-module.js
+not_node_modules/file.js
+regular-module.js
+"
+`;
+
+exports[`ignores node_modules by default 1`] = `
+"not_node_modules/file.js
+regular-module.js
+"
+`;
+
+exports[`ignores node_modules by default for file list 1`] = `
+"not_node_modules/file.js
+regular-module.js
+"
+`;
diff --git a/tests_integration/__tests__/with-node-modules.js b/tests_integration/__tests__/with-node-modules.js
new file mode 100644
index 00000000..de23fcaa
--- /dev/null
+++ b/tests_integration/__tests__/with-node-modules.js
@@ -0,0 +1,42 @@
+"use strict";
+
+const runPrettier = require("../runPrettier");
+
+test("ignores node_modules by default", () => {
+  const result = runPrettier("cli/with-node-modules", ["**/*.js", "-l"]);
+
+  expect(result.stdout).toMatchSnapshot();
+});
+
+test("doesn't ignore node_modules with --with-node-modules flag", () => {
+  const result = runPrettier("cli/with-node-modules", [
+    "**/*.js",
+    "-l",
+    "--with-node-modules"
+  ]);
+
+  expect(result.stdout).toMatchSnapshot();
+});
+
+test("ignores node_modules by default for file list", () => {
+  const result = runPrettier("cli/with-node-modules", [
+    "node_modules/node-module.js",
+    "not_node_modules/file.js",
+    "regular-module.js",
+    "-l"
+  ]);
+
+  expect(result.stdout).toMatchSnapshot();
+});
+
+test("doesn't ignore node_modules with --with-node-modules flag for file list", () => {
+  const result = runPrettier("cli/with-node-modules", [
+    "node_modules/node-module.js",
+    "not_node_modules/file.js",
+    "regular-module.js",
+    "-l",
+    "--with-node-modules"
+  ]);
+
+  expect(result.stdout).toMatchSnapshot();
+});
diff --git a/tests_integration/cli/with-node-modules/node_modules/node-module.js b/tests_integration/cli/with-node-modules/node_modules/node-module.js
new file mode 100644
index 00000000..3d0ca1bd
--- /dev/null
+++ b/tests_integration/cli/with-node-modules/node_modules/node-module.js
@@ -0,0 +1,2 @@
+/* eslint-disable */
+'use strict';
diff --git a/tests_integration/cli/with-node-modules/not_node_modules/file.js b/tests_integration/cli/with-node-modules/not_node_modules/file.js
new file mode 100644
index 00000000..3d0ca1bd
--- /dev/null
+++ b/tests_integration/cli/with-node-modules/not_node_modules/file.js
@@ -0,0 +1,2 @@
+/* eslint-disable */
+'use strict';
diff --git a/tests_integration/cli/with-node-modules/regular-module.js b/tests_integration/cli/with-node-modules/regular-module.js
new file mode 100644
index 00000000..3d0ca1bd
--- /dev/null
+++ b/tests_integration/cli/with-node-modules/regular-module.js
@@ -0,0 +1,2 @@
+/* eslint-disable */
+'use strict';
diff --git a/tests_integration/runPrettier.js b/tests_integration/runPrettier.js
new file mode 100644
index 00000000..682b50e6
--- /dev/null
+++ b/tests_integration/runPrettier.js
@@ -0,0 +1,30 @@
+/*
+ * runPrettier – spawns `prettier` process.
+ * Adopted from Jest's integration tests suite.
+ */
+"use strict";
+
+const path = require("path");
+const spawnSync = require("cross-spawn").sync;
+
+const PRETTIER_PATH = path.resolve(__dirname, "../bin/prettier.js");
+
+// return the result of the spawned process:
+//  [ 'status', 'signal', 'output', 'pid', 'stdout', 'stderr',
+//    'envPairs', 'options', 'args', 'file' ]
+function runPrettier(dir, args) {
+  const isRelative = dir[0] !== "/";
+
+  if (isRelative) {
+    dir = path.resolve(__dirname, dir);
+  }
+
+  const result = spawnSync(PRETTIER_PATH, args || [], { cwd: dir });
+
+  result.stdout = result.stdout && result.stdout.toString();
+  result.stderr = result.stderr && result.stderr.toString();
+
+  return result;
+}
+
+module.exports = runPrettier;
diff --git a/yarn.lock b/yarn.lock
index dcfc69b8..a1ded638 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -592,6 +592,14 @@ create-hmac@^1.1.0, create-hmac@^1.1.2:
     create-hash "^1.1.0"
     inherits "^2.0.1"
 
+cross-spawn@^5.1.0:
+  version "5.1.0"
+  resolved "https://registry.yarnpkg.com/cross-spawn/-/cross-spawn-5.1.0.tgz#e8bd0efee58fcff6f8f94510a0a554bbfa235449"
+  dependencies:
+    lru-cache "^4.0.1"
+    shebang-command "^1.2.0"
+    which "^1.2.9"
+
 cryptiles@2.x.x:
   version "2.0.5"
   resolved "https://registry.yarnpkg.com/cryptiles/-/cryptiles-2.0.5.tgz#3bdfecdc608147c1c67202fa291e7dca59eaa3b8"
@@ -1843,6 +1851,13 @@ loose-envify@^1.0.0:
   dependencies:
     js-tokens "^3.0.0"
 
+lru-cache@^4.0.1:
+  version "4.0.2"
+  resolved "https://registry.yarnpkg.com/lru-cache/-/lru-cache-4.0.2.tgz#1d17679c069cda5d040991a09dbc2c0db377e55e"
+  dependencies:
+    pseudomap "^1.0.1"
+    yallist "^2.0.0"
+
 magic-string@^0.16.0:
   version "0.16.0"
   resolved "https://registry.yarnpkg.com/magic-string/-/magic-string-0.16.0.tgz#970ebb0da7193301285fb1aa650f39bdd81eb45a"
@@ -2189,6 +2204,10 @@ prr@~0.0.0:
   version "0.0.0"
   resolved "https://registry.yarnpkg.com/prr/-/prr-0.0.0.tgz#1a84b85908325501411853d0081ee3fa86e2926a"
 
+pseudomap@^1.0.1:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/pseudomap/-/pseudomap-1.0.2.tgz#f052a28da70e618917ef0a8ac34c1ae5a68286b3"
+
 public-encrypt@^4.0.0:
   version "4.0.0"
   resolved "https://registry.yarnpkg.com/public-encrypt/-/public-encrypt-4.0.0.tgz#39f699f3a46560dd5ebacbca693caf7c65c18cc6"
@@ -2467,6 +2486,16 @@ sha.js@^2.3.6:
   dependencies:
     inherits "^2.0.1"
 
+shebang-command@^1.2.0:
+  version "1.2.0"
+  resolved "https://registry.yarnpkg.com/shebang-command/-/shebang-command-1.2.0.tgz#44aac65b695b03398968c39f363fee5deafdf1ea"
+  dependencies:
+    shebang-regex "^1.0.0"
+
+shebang-regex@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/shebang-regex/-/shebang-regex-1.0.0.tgz#da42f49740c0b42db2ca9728571cb190c98efea3"
+
 shelljs@^0.7.5:
   version "0.7.7"
   resolved "https://registry.yarnpkg.com/shelljs/-/shelljs-0.7.7.tgz#b2f5c77ef97148f4b4f6e22682e10bba8667cff1"
@@ -2782,7 +2811,7 @@ which-module@^1.0.0:
   version "1.0.0"
   resolved "https://registry.yarnpkg.com/which-module/-/which-module-1.0.0.tgz#bba63ca861948994ff307736089e3b96026c2a4f"
 
-which@^1.2.12:
+which@^1.2.12, which@^1.2.9:
   version "1.2.14"
   resolved "https://registry.yarnpkg.com/which/-/which-1.2.14.tgz#9a87c4378f03e827cecaf1acdf56c736c01c14e5"
   dependencies:
@@ -2840,6 +2869,10 @@ y18n@^3.2.1:
   version "3.2.1"
   resolved "https://registry.yarnpkg.com/y18n/-/y18n-3.2.1.tgz#6d15fba884c08679c0d77e88e7759e811e07fa41"
 
+yallist@^2.0.0:
+  version "2.1.2"
+  resolved "https://registry.yarnpkg.com/yallist/-/yallist-2.1.2.tgz#1c11f9218f076089a47dd512f93c6699a6a81d52"
+
 yargs-parser@^5.0.0:
   version "5.0.0"
   resolved "https://registry.yarnpkg.com/yargs-parser/-/yargs-parser-5.0.0.tgz#275ecf0d7ffe05c77e64e7c86e4cd94bf0e1228a"