Distributed systems must provide certain fundamental facilities, including communication, protection, resource management, reliability, and process (computation) abstraction. Current designs for distributed systems tend to focus on only one or two of these issues; support for multiprocess structures has been especially neglected. This paper describes the design of HPC, an object-oriented model of interprocess relationships for distributed systems that addresses all of these fundamental services. The major novelties of HPC lie in the extension of the process abstraction to collections of processes and the provision of a rich set of structuring mechanisms for distributed computations. An important aspect of the model is that it results in the ability to maintain and exploit execution context for managing processes in a distributed computation.