This document provides an overview of grid computing. It defines grid computing as combining computer resources from multiple administrative domains to reach a common goal. It discusses key grid computing concepts like types of resources (computation, storage, communication, software/licenses), jobs and applications, and grid software components for management and distributed grid management. The document also distinguishes between inter-grid and intra-grid systems, with grids able to be built at various scales from just a few machines to globally spanning hierarchies.