Android is a platform delivered by Google within the Open Handset Alliance as a complete set of software for mobile devices: an operating system, middleware and key mobile applications. Built on the open Linux Kernel, it is customized to optimize memory and hardware resources in a mobile environment and promises to be a formidable force in the industry.
Developing applications for Android devices is facilitated by a group of tools that are provided with the SDK. You can access these tools through an Eclipse plugin called ADT (Android Development Tools) or from the command line. Developing with Eclipse is the preferred method because it can directly invoke the tools that you need while developing applications.