diff --git a/types/custom-functions-runtime/custom-functions-runtime-tests.ts b/types/custom-functions-runtime/custom-functions-runtime-tests.ts
new file mode 100644
index 0000000000..335e5a1f95
--- /dev/null
+++ b/types/custom-functions-runtime/custom-functions-runtime-tests.ts
@@ -0,0 +1,33 @@
+/* Note that this is a sample function for the purpose of running the below CustomFunctionsMappings test */
+function ADD10(n: number) {
+    return n + 10;
+}
+
+CustomFunctionMappings = {
+    addTen: ADD10
+};
+
+async function getStockValues(ticker: string, handler: CustomFunctions.StreamingHandler<number>) {
+    const dollars = await (await fetch(`myService.com/prices/${ticker}`)).json();
+        handler.setResult(dollars);
+}
+
+async function getStockValuesOneTime(ticker: string, handler: CustomFunctions.CancelableHandler) {
+    let shouldStop = false;
+    handler.onCanceled = () => shouldStop = true;
+    await pause(1000);
+
+    if (shouldStop) {
+        return null;
+    }
+
+      const dollars = await (await fetch(`myService.com/prices/${ticker}`)).json();
+        return dollars;
+}
+
+async function getStockValuesNowWithNoCancelling(ticker: string) {
+    const dollars = await (await fetch(`myService.com/prices/${ticker}`)).json();
+    return dollars;
+}
+
+declare function pause(ms: number): Promise<void>;
diff --git a/types/custom-functions-runtime/index.d.ts b/types/custom-functions-runtime/index.d.ts
new file mode 100644
index 0000000000..e233a869fd
--- /dev/null
+++ b/types/custom-functions-runtime/index.d.ts
@@ -0,0 +1,30 @@
+// Type definitions for Custom Functions 1.4
+// Project: http://dev.office.com
+// Definitions by: OfficeDev <https://github.com/OfficeDev>, Michael Zlatkovsky <https://github.com/Zlatkovsky>, Michelle Scharlock <https://github.com/mscharlock>
+// Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
+// TypeScript Version: 2.4
+
+/*
+office-js
+Copyright (c) Microsoft Corporation
+*/
+
+declare let CustomFunctionMappings: { [key: string]: Function };
+
+declare namespace CustomFunctions {
+    interface StreamingHandler<T> extends CancelableHandler {
+        /*
+        * Sets the returned result for a streaming custom function.
+        * @beta
+        */
+        setResult: (value: T) => void;
+    }
+
+    interface CancelableHandler {
+        /*
+        * Handles what should occur when a custom function is canceled.
+        * @beta
+        */
+        onCanceled: () => void;
+    }
+}
diff --git a/types/custom-functions-runtime/tsconfig.json b/types/custom-functions-runtime/tsconfig.json
new file mode 100644
index 0000000000..3c8cbbaf27
--- /dev/null
+++ b/types/custom-functions-runtime/tsconfig.json
@@ -0,0 +1,23 @@
+{
+    "compilerOptions": {
+        "module": "commonjs",
+        "lib": [
+            "es6", 
+            "dom"
+        ],
+        "noImplicitAny": true,
+        "noImplicitThis": true,
+        "strictNullChecks": false,
+        "strictFunctionTypes": true,
+        "baseUrl": "../",
+        "typeRoots": ["../"],
+        "types": [],
+        "noEmit": true,
+        "forceConsistentCasingInFileNames": true,
+        "target": "es6"
+    },
+    "files": [
+        "index.d.ts",
+        "custom-functions-runtime-tests.ts"
+    ]
+}
diff --git a/types/custom-functions-runtime/tslint.json b/types/custom-functions-runtime/tslint.json
new file mode 100644
index 0000000000..a62d0d4e68
--- /dev/null
+++ b/types/custom-functions-runtime/tslint.json
@@ -0,0 +1,6 @@
+{
+    "extends": "dtslint/dt.json",
+    "rules": {
+        "ban-types": false
+    }
+}