diff --git a/types/csso/csso-tests.ts b/types/csso/csso-tests.ts
new file mode 100644
index 0000000000..74e0b51dd9
--- /dev/null
+++ b/types/csso/csso-tests.ts
@@ -0,0 +1,40 @@
+import csso = require('csso');
+
+csso.minify('.test { color: #ff0000; }').css;
+csso.minify('.test { color: #ff0000; }').map;
+csso.minify('.test { color: #ff0000; }', {
+    sourceMap: true,
+    filename: '',
+    debug: true,
+    beforeCompress: () => {},
+    afterCompress: () => {},
+    restructure: false,
+    forceMediaMerge: true,
+    clone: false,
+    comments: '',
+    logger: () => {}
+});
+
+csso.minifyBlock('color: rgba(255, 0, 0, 1); color: #ff0000').css;
+csso.minifyBlock('color: rgba(255, 0, 0, 1); color: #ff0000').map;
+csso.minifyBlock('color: rgba(255, 0, 0, 1); color: #ff0000', {
+    sourceMap: true,
+    filename: '',
+    debug: true,
+    beforeCompress: () => {},
+    afterCompress: () => {},
+    restructure: false,
+    forceMediaMerge: true,
+    clone: false,
+    comments: '',
+    logger: () => {}
+});
+
+csso.compress({}).ast;
+csso.compress({}, {
+    restructure: false,
+    forceMediaMerge: true,
+    clone: false,
+    comments: '',
+    logger: () => {}
+}).ast;
diff --git a/types/csso/index.d.ts b/types/csso/index.d.ts
new file mode 100644
index 0000000000..f89f395129
--- /dev/null
+++ b/types/csso/index.d.ts
@@ -0,0 +1,107 @@
+// Type definitions for csso 3.5
+// Project: https://github.com/css/csso
+// Definitions by: Christian Rackerseder <https://github.com/screendriver>
+// Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
+// TypeScript Version: 2.6
+
+declare namespace csso {
+    interface Result {
+        /**
+         * Resulting CSS.
+         */
+        css: string;
+        /**
+         * Instance of SourceMapGenerator or null.
+         */
+        map: object | null;
+    }
+
+    interface CompressOptions {
+        /**
+         * Disable or enable a structure optimisations.
+         * @default true
+         */
+        restructure?: boolean;
+        /**
+         * Enables merging of @media rules with the same media query by splitted by other rules.
+         * The optimisation is unsafe in general, but should work fine in most cases. Use it on your own risk.
+         * @default false
+         */
+        forceMediaMerge?: boolean;
+        /**
+         * Transform a copy of input AST if true. Useful in case of AST reuse.
+         * @default false
+         */
+        clone?: boolean;
+        /**
+         * Specify what comments to leave:
+         * - 'exclamation' or true – leave all exclamation comments
+         * - 'first-exclamation' – remove every comment except first one
+         * - false – remove all comments
+         * @default true
+         */
+        comments?: string | boolean;
+        /**
+         * Usage data for advanced optimisations.
+         */
+        usage?: object;
+        /**
+         * Function to track every step of transformation.
+         */
+        logger?: () => void;
+    }
+
+    interface MinifyOptions {
+        /**
+         * Generate a source map when true.
+         * @default false
+         */
+        sourceMap?: boolean;
+        /**
+         * Filename of input CSS, uses for source map generation.
+         * @default '<unknown>'
+         */
+        filename?: string;
+        /**
+         * Output debug information to stderr.
+         * @default false
+         */
+        debug?: boolean;
+        /**
+         * Called right after parse is run.
+         */
+        beforeCompress?: BeforeCompressFn | BeforeCompressFn[];
+        /**
+         * Called right after compress() is run.
+         */
+        afterCompress?: AfterCompressFn | AfterCompressFn[];
+        restructure?: boolean;
+    }
+
+    type BeforeCompressFn = (ast: object, options: CompressOptions) => void;
+    type AfterCompressFn = (compressResult: string, options: CompressOptions) => void;
+}
+
+interface Csso {
+    /**
+     * Minify source CSS passed as String
+     * @param source
+     * @param options
+     */
+    minify(source: string, options?: csso.MinifyOptions & csso.CompressOptions): csso.Result;
+
+    /**
+     * The same as minify() but for list of declarations. Usually it's a style attribute value.
+     * @param source
+     * @param options
+     */
+    minifyBlock(source: string, options?: csso.MinifyOptions & csso.CompressOptions): csso.Result;
+
+    /**
+     * Does the main task – compress an AST.
+     */
+    compress(ast: object, options?: csso.CompressOptions): { ast: object };
+}
+
+declare const csso: Csso;
+export = csso;
diff --git a/types/csso/tsconfig.json b/types/csso/tsconfig.json
new file mode 100644
index 0000000000..9ed6695bc9
--- /dev/null
+++ b/types/csso/tsconfig.json
@@ -0,0 +1,23 @@
+{
+    "compilerOptions": {
+        "module": "commonjs",
+        "lib": [
+            "es6"
+        ],
+        "noImplicitAny": true,
+        "noImplicitThis": true,
+        "strictNullChecks": true,
+        "strictFunctionTypes": true,
+        "baseUrl": "../",
+        "typeRoots": [
+            "../"
+        ],
+        "types": [],
+        "noEmit": true,
+        "forceConsistentCasingInFileNames": true
+    },
+    "files": [
+        "index.d.ts",
+        "csso-tests.ts"
+    ]
+}
diff --git a/types/csso/tslint.json b/types/csso/tslint.json
new file mode 100644
index 0000000000..3db14f85ea
--- /dev/null
+++ b/types/csso/tslint.json
@@ -0,0 +1 @@
+{ "extends": "dtslint/dt.json" }