diff --git a/types/webpack-merge/index.d.ts b/types/webpack-merge/index.d.ts
index a939a2ed53..421737ccaf 100644
--- a/types/webpack-merge/index.d.ts
+++ b/types/webpack-merge/index.d.ts
@@ -1,25 +1,34 @@
-// Type definitions for webpack-merge
+// Type definitions for webpack-merge 4.1
 // Project: https://github.com/survivejs/webpack-merge
-// Definitions by: Simon Hartcher <https://github.com/deevus>
+// Definitions by: Simon Hartcher <https://github.com/deevus>, Matt Traynham <https://github.com/mtraynham>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
-///<reference types="webpack" />
+import webpack = require('webpack');
 
-declare module "webpack-merge" {
-    import { Configuration } from "webpack";
+export = webpackMerge;
+
+declare const webpackMerge: webpackMerge.WebpackMerge;
+
+declare namespace webpackMerge {
+    type CustomizeArrayFunction = (a: any[], b: any[], key: string) => any[] | null | undefined;
+    type CustomizeObjectFunction = (a: {}, b: {}, key: string) => {} | null | undefined;
+    type UniqueFunction = (field: string, fields: string[], keyFn: (field: any) => string) => CustomizeArrayFunction;
+    interface CustomizeOptions {
+        customizeArray?: CustomizeArrayFunction | UniqueFunction;
+        customizeObject?: CustomizeObjectFunction;
+    }
+    type ConfigurationMergeFunction = (...configs: webpack.Configuration[]) => webpack.Configuration;
+    type ConfigurationMergeConfigFunction = (customizeOptions: CustomizeOptions) => ConfigurationMergeFunction;
+    type MergeFunction = ConfigurationMergeFunction | ConfigurationMergeConfigFunction;
+    type MergeStrategy = 'prepend' | 'append' | 'replace';
 
     interface WebpackMerge {
-        /**
-         * Merge multiple webpack configurations into one.
-         */
-        (...configs: Configuration[]): Configuration;
-
-        /**
-         * Merge multiple webpack configurations into one, with smart merging of loaders.
-         */
-        smart(...configs: Configuration[]): Configuration;
+        (...configs: webpack.Configuration[]): webpack.Configuration;
+        (customizeOptions: CustomizeOptions): ConfigurationMergeFunction;
+        unique: UniqueFunction;
+        smart: ConfigurationMergeFunction;
+        multiple: ConfigurationMergeFunction;
+        strategy(options: {[field: string]: MergeStrategy}): ConfigurationMergeFunction;
+        smartStrategy(options: {[key: string]: MergeStrategy}): ConfigurationMergeFunction;
     }
-
-    const merge: WebpackMerge;
-    export = merge;
 }
diff --git a/types/webpack-merge/tsconfig.json b/types/webpack-merge/tsconfig.json
index f2368dc89d..78589b444b 100644
--- a/types/webpack-merge/tsconfig.json
+++ b/types/webpack-merge/tsconfig.json
@@ -6,7 +6,7 @@
         ],
         "noImplicitAny": true,
         "noImplicitThis": true,
-        "strictNullChecks": false,
+        "strictNullChecks": true,
         "baseUrl": "../",
         "typeRoots": [
             "../"
@@ -19,4 +19,4 @@
         "index.d.ts",
         "webpack-merge-tests.ts"
     ]
-}
\ No newline at end of file
+}
diff --git a/types/webpack-merge/tslint.json b/types/webpack-merge/tslint.json
new file mode 100644
index 0000000000..3db14f85ea
--- /dev/null
+++ b/types/webpack-merge/tslint.json
@@ -0,0 +1 @@
+{ "extends": "dtslint/dt.json" }
diff --git a/types/webpack-merge/v0/index.d.ts b/types/webpack-merge/v0/index.d.ts
new file mode 100644
index 0000000000..a939a2ed53
--- /dev/null
+++ b/types/webpack-merge/v0/index.d.ts
@@ -0,0 +1,25 @@
+// Type definitions for webpack-merge
+// Project: https://github.com/survivejs/webpack-merge
+// Definitions by: Simon Hartcher <https://github.com/deevus>
+// Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
+
+///<reference types="webpack" />
+
+declare module "webpack-merge" {
+    import { Configuration } from "webpack";
+
+    interface WebpackMerge {
+        /**
+         * Merge multiple webpack configurations into one.
+         */
+        (...configs: Configuration[]): Configuration;
+
+        /**
+         * Merge multiple webpack configurations into one, with smart merging of loaders.
+         */
+        smart(...configs: Configuration[]): Configuration;
+    }
+
+    const merge: WebpackMerge;
+    export = merge;
+}
diff --git a/types/webpack-merge/v0/tsconfig.json b/types/webpack-merge/v0/tsconfig.json
new file mode 100644
index 0000000000..aedaa9a44e
--- /dev/null
+++ b/types/webpack-merge/v0/tsconfig.json
@@ -0,0 +1,26 @@
+{
+    "compilerOptions": {
+        "module": "commonjs",
+        "lib": [
+            "es6"
+        ],
+        "noImplicitAny": true,
+        "noImplicitThis": true,
+        "strictNullChecks": false,
+        "baseUrl": "../../",
+        "typeRoots": [
+            "../../"
+        ],
+        "types": [],
+        "paths": {
+            "webpack-merge": ["webpack-merge/v0"],
+            "webpack-merge/*": ["webpack-merge/v0/*"]
+        },
+        "noEmit": true,
+        "forceConsistentCasingInFileNames": true
+    },
+    "files": [
+        "index.d.ts",
+        "webpack-merge-tests.ts"
+    ]
+}
\ No newline at end of file
diff --git a/types/webpack-merge/v0/webpack-merge-tests.ts b/types/webpack-merge/v0/webpack-merge-tests.ts
new file mode 100644
index 0000000000..4c9c4adca4
--- /dev/null
+++ b/types/webpack-merge/v0/webpack-merge-tests.ts
@@ -0,0 +1,12 @@
+import merge = require("webpack-merge");
+import { Configuration } from "webpack";
+
+const a: Configuration = {
+    entry: "test.js"
+}
+const b: Configuration = {
+    devtool: "source-map"
+}
+
+const c = merge(a, b);
+const d = merge.smart(a, b);
diff --git a/types/webpack-merge/webpack-merge-tests.ts b/types/webpack-merge/webpack-merge-tests.ts
index 4c9c4adca4..d7180a6950 100644
--- a/types/webpack-merge/webpack-merge-tests.ts
+++ b/types/webpack-merge/webpack-merge-tests.ts
@@ -1,12 +1,61 @@
-import merge = require("webpack-merge");
-import { Configuration } from "webpack";
+import _ = require('lodash');
+import { Configuration, HotModuleReplacementPlugin, Plugin } from 'webpack';
+import webpackMerge = require('webpack-merge');
 
 const a: Configuration = {
-    entry: "test.js"
-}
+    entry: 'test.js'
+};
 const b: Configuration = {
-    devtool: "source-map"
-}
+    devtool: 'source-map'
+};
 
-const c = merge(a, b);
-const d = merge.smart(a, b);
+const c: Configuration = webpackMerge(a, b);
+const d: Configuration = webpackMerge.smart(a, b);
+const e: Configuration = webpackMerge.multiple(a, b);
+const f: Configuration = webpackMerge(
+    {
+        customizeArray(x: any[], y: any[], key: string): any[] | undefined {
+            if (key === 'extensions') {
+                return _.uniq([...x, ...y]);
+            }
+            // Fall back to default merging
+            return undefined;
+        },
+        customizeObject(x: {}, y: {}, key: string): {} | undefined {
+            if (key === 'module') {
+                // Custom merging
+                return _.merge({}, x, y);
+            }
+
+            // Fall back to default merging
+            return undefined;
+        }
+    }
+)(a, b);
+const g: Configuration = webpackMerge({
+    customizeArray: webpackMerge.unique(
+        'plugins',
+        ['HotModuleReplacementPlugin'],
+        (plugin: Plugin) => plugin.constructor && plugin.constructor.name
+    )
+})({
+    plugins: [
+        new HotModuleReplacementPlugin()
+    ]
+}, {
+    plugins: [
+        new HotModuleReplacementPlugin()
+    ]
+});
+const h: Configuration = webpackMerge.strategy(
+    {
+        entry: 'prepend', // or 'replace', defaults to 'append'
+        'module.loaders': 'prepend'
+    }
+)(a, b);
+const i: Configuration = webpackMerge.smartStrategy(
+    {
+        entry: 'prepend', // or 'replace'
+        'module.loaders': 'prepend'
+    }
+)(a, b);