The App, which was already released for Windows Phone and Android, allows users to control a variety of Xbox features from their phones or tablets. There's plenty of functionality ranging from navigating their dashboard to typing on their Xbox 360's to pausing videos.
Of course, SmartGlass's main functionality comes in the form of interactive experiences, sent straight from the game to your SmartGlass-enabled device - a feature that Halo 4 is laden with. When you find interesting data, like a new weapon, it'll be sent straight to your SmartGlass app, where you can read about it in-depth.
So if you've got an iOS, Android, or Windows Phone device head to your prospective app market and download SmartGlass. It's free on every platform.