This book constitutes the refereed proceedings of the 6th International Workshop on Interactive Distributed Multimedia Systems and Telecommunication Services, IDMS'99, held in Toulouse, France in October 1999. The 25 revised full papers presented together with three position papers and three abstracts of invited talks were carefully reviewed and selected from a total of 84 submissions. The book is divided in topical sections on network QoS, application QoS, mbone and multicast, adaptive applications and networks, new trends in IDMS, advances in coding, conferencing, and video servers.