Abstract machine models have played an important, although frequently unacknowledged, role in the development of modern computing systems. They provide a precise definition of vital concepts, allow system complexity to be managed by providing appropriate views of the activity under consideration, enable reasoning about the correctness and quantitative performance of proposed problem solutions, and encourage communication through a common medium of expression. This volume attempts to demonstrate the importance of that role in contemporary systems, in conjunction with parallel and distributed computing. The proponents of parallel and distributed models have traditionally considered themselves to be separate. However, this text indicates a significant contemporary interest in both of these communities in a common hardware model: a set of workstation-class machines connected in a high-performance network. It therefore shows that the traditional parallel/distributed distinction appears to be under threat.