The Grid philosophy, proposed by Ian Foster, posits three main requirements. First, a grid isn't subject to centralized control. Second, a grid is based on standard, open, and general-purpose interfaces and protocols. Third, the interfaces and protocols provide some level of quality of service, in terms of security, throughput, response time, or the coordinated use of different resource types. Some current grid architectures ignore the first two requirements to get higher levels of quality of service—mainly performance and reliability—for a given application scope. However, we believe that these two requirements are the key to a grid's success. The loosely coupled model provides the required trade-off to foster the diffusion of grid technologies.