This book constitutes the thoroughly revised proceedings of the Fourth International Workshop on Network and Operating System Support for Digital Audio and Video (NOSSDAV '93), held in Lancaster, UK in November 1993. The 24 papers presented in the volume were carefully selected from more than 100 submissions. In addition, the book contains an introduction by the editors as well as a summary of the discussions that occurred during the workshop and a record of the panel and work-in-progress session. The book is organized into chapters on end system architecture, operating system support, high speed networking, quality of service, protocol issues, resource reservation in heterogeneous networks, and storage servers and multicast.