diff --git a/gluon.d.ts b/gluon.d.ts
index 24b3313..c59da16 100644
--- a/gluon.d.ts
+++ b/gluon.d.ts
@@ -1,3 +1,64 @@
+type WindowApi = {
+  /**
+   * Evaluate a string or function in the web context.
+   * @returns Return value of expression given.
+   */
+  eval: (
+    /** String or function to evaluate. */
+    expression: string|Function
+  ) => Promise<any>
+};
+
+type IPCApi = {
+  /**
+   * Send an IPC event to the web context.
+   * @returns Replied event data (null by default).
+   */
+  send(
+    /** Type of event to send. */
+    type: string,
+
+    /** Data of event to send. */
+    data: any
+  ): Promise<any?>,
+
+  /**
+   * Subscribe to IPC events of a specific type with a callback.
+   */
+  on(
+    /** Type of event to handle. */
+    type: string,
+
+    /**
+     * Ran whenever an IPC event of type specified is recieved. Should return optionally with what to reply with.
+     * @returns Optionally with what to reply with, otherwise null by default.
+     */
+    callback: (data: any) => any
+  ): void
+};
+
+type CDPApi = {
+  /**
+   * Send a CDP command to the browser.
+   * {@link https://chromedevtools.github.io/devtools-protocol/ Chrome DevTools Protocol Documentation}
+   * @returns Result of command from browser.
+   */
+  send(
+    /** Method of CDP command. */
+    method: string,
+
+    /** Parameters of CDP command. */
+    params: Object?
+  ): Promise<any>
+};
+
+type Window = {
+  window: WindowApi,
+  ipc: IPCApi,
+  cdp: CDPApi
+};
+
+
 /** A browser that Gluon supports. */
 type Browser = 'chrome'|'chrome_canary'|'chromium'|'edge'|'firefox'|'firefox_nightly';
 
@@ -19,4 +80,4 @@ export function open(
 
   /** Additional options for opening. */
   options: OpenOptions
-);
\ No newline at end of file
+): Promise<Window>;
\ No newline at end of file
diff --git a/roadmap.md b/roadmap.md
index 4ca4c85..b9baef3 100644
--- a/roadmap.md
+++ b/roadmap.md
@@ -5,6 +5,7 @@
 
 ## December 2022 - January 2023
 - [X] Total internal rewrite
+- [X] Type definitions
 - [ ] "Hibernation" feasibility study
 - [ ] Automated PR/commit CI testing
 - [ ] System Tray API