The World Wide Web has become pervasive in many facets of our professional and personal lives during the past 10 years. Today, another Internet revolution is emerging: Grid Computing. While the Web offers easy access to mostly static information via Hypertext, the Grid adds another fundamental layer by enabling access to and use of the underlying resources. Based on widely accepted grid and web services standards, resources including computers, storage, scientific instruments and experiments, applications, data, and middleware services communicate with each other and deliver results back to the user. These resources are part of a single service-oriented architecture, called OGSA, the Open Grid Services Architecture. For the past several years, early adopters in research and industry have been building and operating prototypes of grids for global communities, virtual organizations, and within enterprises..