The thoroughly refereed postproceedings of the International Workshop on Architectures for Quality of Service in the Internet, Art-QoS 2003, held in Warsaw, Poland, in March 2003. The 22 revised full papers presented were carefully reviewed and selected for inclusion in the book. The papers are organized in topical sections on architectures for next generation networks, architectures and services, signalling, admission control, AQUILA-resource control, AQUILA-QoS at work, MPLS traffic engineering, and traffic control mechanisms.