diff --git a/packages/react-scripts/config/paths.js b/packages/react-scripts/config/paths.js
index d15b16a0544..18307aee7f1 100644
--- a/packages/react-scripts/config/paths.js
+++ b/packages/react-scripts/config/paths.js
@@ -10,14 +10,8 @@
 // @remove-on-eject-end
 
 var path = require('path');
-var fs = require('fs');
 
-// Make sure any symlinks in the project folder are resolved:
-// https://github.com/facebookincubator/create-react-app/issues/637
-var appDirectory = fs.realpathSync(process.cwd());
-function resolveApp(relativePath) {
-  return path.resolve(appDirectory, relativePath);
-}
+var resolveApp = require('../utils/resolveApp');
 
 // We support resolving modules according to `NODE_PATH`.
 // This lets you use absolute paths in imports inside large monorepos:
diff --git a/packages/react-scripts/package.json b/packages/react-scripts/package.json
index d0f22bdd934..45a73473a6a 100644
--- a/packages/react-scripts/package.json
+++ b/packages/react-scripts/package.json
@@ -52,6 +52,7 @@
     "http-proxy-middleware": "0.17.2",
     "jest": "17.0.2",
     "json-loader": "0.5.4",
+    "lodash": "^4.17.2",
     "object-assign": "4.1.0",
     "path-exists": "2.1.0",
     "postcss-loader": "1.0.0",
diff --git a/packages/react-scripts/scripts/build.js b/packages/react-scripts/scripts/build.js
index 8e4141be8bc..f4d87890c9f 100644
--- a/packages/react-scripts/scripts/build.js
+++ b/packages/react-scripts/scripts/build.js
@@ -25,12 +25,21 @@ var pathExists = require('path-exists');
 var filesize = require('filesize');
 var gzipSize = require('gzip-size').sync;
 var webpack = require('webpack');
-var config = require('../config/webpack.config.prod');
 var paths = require('../config/paths');
 var checkRequiredFiles = require('react-dev-utils/checkRequiredFiles');
 var recursive = require('recursive-readdir');
 var stripAnsi = require('strip-ansi');
 
+var getWebpackConfig = require('../utils/getWebpackConfig');
+
+var config;
+
+config = require('../config/webpack.config.prod');
+
+// @remove-on-eject-begin
+config = getWebpackConfig('../config/webpack.config.prod');
+// @remove-on-eject-end
+
 var useYarn = pathExists.sync(paths.yarnLockFile);
 
 // Warn and crash if required files are missing
diff --git a/packages/react-scripts/scripts/eject.js b/packages/react-scripts/scripts/eject.js
index a2bd4961026..411c1ce2b5e 100644
--- a/packages/react-scripts/scripts/eject.js
+++ b/packages/react-scripts/scripts/eject.js
@@ -58,6 +58,7 @@ prompt(
     path.join('config', 'webpack.config.prod.js'),
     path.join('config', 'jest', 'CSSStub.js'),
     path.join('config', 'jest', 'FileStub.js'),
+    path.join('utils', 'resolveApp.js'),
     path.join('scripts', 'build.js'),
     path.join('scripts', 'start.js'),
     path.join('scripts', 'test.js')
diff --git a/packages/react-scripts/scripts/start.js b/packages/react-scripts/scripts/start.js
index 752bd8a08a8..21457c44a6f 100644
--- a/packages/react-scripts/scripts/start.js
+++ b/packages/react-scripts/scripts/start.js
@@ -30,9 +30,18 @@ var getProcessForPort = require('react-dev-utils/getProcessForPort');
 var openBrowser = require('react-dev-utils/openBrowser');
 var prompt = require('react-dev-utils/prompt');
 var pathExists = require('path-exists');
-var config = require('../config/webpack.config.dev');
 var paths = require('../config/paths');
 
+var getWebpackConfig = require('../utils/getWebpackConfig');
+
+var config;
+
+config = require('../config/webpack.config.dev');
+
+// @remove-on-eject-begin
+config = getWebpackConfig('../config/webpack.config.dev');
+// @remove-on-eject-end
+
 var useYarn = pathExists.sync(paths.yarnLockFile);
 var cli = useYarn ? 'yarn' : 'npm';
 var isInteractive = process.stdout.isTTY;
diff --git a/packages/react-scripts/utils/getWebpackConfig.js b/packages/react-scripts/utils/getWebpackConfig.js
new file mode 100644
index 00000000000..81cfef0ca22
--- /dev/null
+++ b/packages/react-scripts/utils/getWebpackConfig.js
@@ -0,0 +1,60 @@
+var mergeWith = require('lodash/mergeWith');
+var resolveApp = require('./resolveApp');
+var paths = require('../config/paths');
+
+function customizer(objValue, srcValue) {
+  if (Array.isArray(objValue)) {
+    return objValue.concat(srcValue);
+  }
+}
+
+function firstLevelCustomizer(objValue, srcValue, paramName) {
+  var array = customizer(objValue, srcValue, paramName);
+
+  if (array) return array;
+
+  if (paramName === 'eslint' && srcValue.configFile) {
+    srcValue.configFile = resolveApp(srcValue.configFile);
+  }
+
+  if (typeof srcValue === 'object') {
+    return mergeWith(objValue, srcValue, customizer);
+  }
+}
+
+function getWebpackConfig(defaultPath) {
+  var configPath = resolveApp(process.env.WEBPACK_REPLACE, defaultPath);
+
+  var initialConfig = require(configPath);
+  var extendConfig = resolveApp(process.env.WEBPACK_MERGE);
+
+  var resultConfig = extendConfig ? mergeWith(
+    initialConfig,
+    require(extendConfig),
+    firstLevelCustomizer
+  ) : initialConfig;
+
+  var babelConfigPath = resolveApp(process.env.BABEL_REPLACE);
+
+  if (babelConfigPath) {
+    var loaderBabel = resultConfig.module.loaders.filter(function (loader) {
+      return loader.loader === 'babel';
+    })[0];
+
+    if (!loaderBabel) {
+      loaderBabel = {
+        test: /\.(js|jsx)$/,
+        include: paths.appSrc,
+        loader: 'babel'
+      };
+
+      resultConfig.module.loaders.push(loaderBabel);
+    }
+
+    loaderBabel.query = require(babelConfigPath);
+  }
+
+  return resultConfig;
+}
+
+module.exports = getWebpackConfig;
diff --git a/packages/react-scripts/utils/resolveApp.js b/packages/react-scripts/utils/resolveApp.js
new file mode 100644
index 00000000000..1690347d602
--- /dev/null
+++ b/packages/react-scripts/utils/resolveApp.js
@@ -0,0 +1,13 @@
+var fs = require('fs');
+var path = require('path');
+
+// Make sure any symlinks in the project folder are resolved:
+// https://github.com/facebookincubator/create-react-app/issues/637
+var appDirectory = fs.realpathSync(process.cwd());
+function resolveApp(relativePath, defaultPath) {
+  return relativePath ?
+    path.resolve(appDirectory, relativePath) :
+    defaultPath;
+}
+
+module.exports = resolveApp;