This paper discusses several important performance problems in the design of local-area networks. The questions discussed relate to various aspects of architecture, design, and implementation: (1) the delaythroughput characteristics of the medium access protocols, (2) the performance of local-area networks on which a file server provides file storage and retrieval services to intelligent workstations, and (3) timing problems in local-area network adapters. Since the paper does not primarily addressth e performance analyst, it is descriptive in nature; analytic details are omitted in favor of a more intuitive explanation of the relevant effects.