This text constitutes the thoroughly refereed post-workshop proceedings of the 4th International Workshop on Communication, Architecture, and Applications for Network-Based Parallel Computing, CANPC 2000, held in Tolouse, France in January 2000. The 12 revised full papers presented were carefully reviewed and selected for inclusion in the book. The papers are organized in sections on program development and execution support, network router architecture, system support for communication abstractions, and network software and interface architecture.