Most modern network protocols give adequate support for traditional applications such as file transfer and remote login. Distributed applications, however, have different requirements 1993. Instead of using ad hoc protocols to meet each of the new requirements, we have designed a new protocol, called the Fast Local Internet Protocol (FLIP), that provides a clean and simple integrated approach to these new requirements. FLIP is an unreliable message protocol that provides both point-to-point communication and multicast communication, and requires almost no network management. Furthermore, by using FLIP we have simplified higher-level protocols such as remote procedure call and group communication, and enhanced support for process migration and security. A prototype implementation of FLIP has been built as part of the new kernel for the Amoeba distributed operating system, and is in daily use. Measurements of its performance are presented. © 1993, ACM. All rights reserved.