diff --git a/packages/babel-cli/src/_babel-node.js b/packages/babel-cli/src/_babel-node.js
index 28b62dd2c0..4b9ac5160a 100644
--- a/packages/babel-cli/src/_babel-node.js
+++ b/packages/babel-cli/src/_babel-node.js
@@ -26,7 +26,7 @@ program.option("-e, --eval [script]", "Evaluate script");
 program.option("-p, --print [code]", "Evaluate script and print result");
 program.option("-o, --only [globs]", "A comma-separated list of glob patterns to compile", collect);
 program.option("-i, --ignore [globs]", "A comma-separated list of glob patterns to skip compiling", collect);
-program.option("-x, --extensions [extensions]", "List of extensions to hook into [.es6,.js,.es,.jsx]", collect);
+program.option("-x, --extensions [extensions]", "List of extensions to hook into [.es6,.js,.es,.jsx,.mjs]", collect);
 program.option("-w, --plugins [string]", "", collect);
 program.option("-b, --presets [string]", "", collect);
 /* eslint-enable max-len */
diff --git a/packages/babel-cli/src/babel/index.js b/packages/babel-cli/src/babel/index.js
index 732ba1b011..42b949f952 100755
--- a/packages/babel-cli/src/babel/index.js
+++ b/packages/babel-cli/src/babel/index.js
@@ -67,7 +67,7 @@ commander.option("-M, --module-ids", "insert an explicit id for modules");
 commander.option("--module-id [string]", "specify a custom name for module ids");
 
 // "babel" command specific arguments that are not passed to babel-core.
-commander.option("-x, --extensions [extensions]", "List of extensions to compile when a directory has been input [.es6,.js,.es,.jsx]", collect);
+commander.option("-x, --extensions [extensions]", "List of extensions to compile when a directory has been input [.es6,.js,.es,.jsx,.mjs]", collect);
 commander.option("-w, --watch", "Recompile files on changes");
 commander.option("--skip-initial-build", "Do not compile files before watching");
 commander.option("-o, --out-file [out]", "Compile all input files into a single file");
diff --git a/packages/babel-core/src/index.js b/packages/babel-core/src/index.js
index eca8d122e7..918929f9bc 100644
--- a/packages/babel-core/src/index.js
+++ b/packages/babel-core/src/index.js
@@ -41,4 +41,4 @@ export {
  * Recommended set of compilable extensions. Not used in babel-core directly, but meant as
  * as an easy source for tooling making use of babel-core.
  */
-export const DEFAULT_EXTENSIONS = Object.freeze([".js", ".jsx", ".es6", ".es"]);
+export const DEFAULT_EXTENSIONS = Object.freeze([".js", ".jsx", ".es6", ".es", ".mjs"]);
diff --git a/packages/babel-register/README.md b/packages/babel-register/README.md
index 413e7a6349..691e8cc2e7 100644
--- a/packages/babel-register/README.md
+++ b/packages/babel-register/README.md
@@ -19,8 +19,8 @@ npm install babel-register --save-dev
 require("babel-register");
 ```
 
-All subsequent files required by node with the extensions `.es6`, `.es`, `.jsx`
-and `.js` will be transformed by Babel.
+All subsequent files required by node with the extensions `.es6`, `.es`, `.jsx`,
+`.mjs`, and `.js` will be transformed by Babel.
 
 <blockquote class="babel-callout babel-callout-info">
   <h4>Polyfill not included</h4>
@@ -64,9 +64,9 @@ require("babel-register")({
   // aren't compiled
   only: /my_es6_folder/,
 
-  // Setting this will remove the currently hooked extensions of .es6, `.es`, `.jsx`
+  // Setting this will remove the currently hooked extensions of `.es6`, `.es`, `.jsx`, `.mjs`
   // and .js so you'll have to add them back if you want them to be used again.
-  extensions: [".es6", ".es", ".jsx", ".js"],
+  extensions: [".es6", ".es", ".jsx", ".js", ".mjs"],
 
   // Setting this to false will disable the cache.
   cache: true