Agile computing may be defined as opportunistically (or on user demand) discovering and taking advantage of available resources in order to improve capability, performance, efficiency, fault tolerance, and survivability. The term agile is used to highlight both the need to quickly react to changes in the environment as well as the need to exploit transient resources only available for short periods of time. Agile computing builds on current research in grid computing, ad-hoc networking, and peer-to-peer resource sharing. This paper describes both the general notion of agile computing as well as one particular approach that exploits mobility of code, data, and computation. Some performance metrics are also suggested to measure the effectiveness of any approach to agile computing.