This document provides an overview of grid computing. It discusses that grid computing enables sharing, selection, and aggregation of distributed resources like supercomputers, storage, and data sources. Grid computing allows for these resources to be used as a unified virtual machine. The document then discusses the services offered by grids including computational, data, application, information, and knowledge services. It also discusses the types of grids like computational grids, data grids, and scavenging grids. Finally, it discusses some of the key advantages of grid computing like making better use of available hardware and idle computing resources.