This document provides an overview of the Android mobile operating system. It describes Android as an open source project led by Google that allows developers to write applications that run on mobile phones. The document outlines Android's features such as its application framework, Dalvik virtual machine, integrated browser, 2D/3D graphics APIs, SQLite database, media codecs, and support for Bluetooth, wireless networks and sensors. It also discusses challenges of developing for Android including limited device hardware and intermittent network connectivity. Finally, it identifies opportunities for Android application development and provides suggestions for sample application ideas.