This book constitutes the refereed proceedings of the 5th International Workshop on Internet Charging and QoS Technologies, ICQT 2006, held in St. Malo, France, June 2006 as an associated workshop of ACM Sigmetrics / IFIP Performance 2006. The book presents eight revised full papers together with a keynote paper, organized in topical sections on economy-driven modeling, auctions, peer-to-peer, and secure billing, addressing vital topics in networking research and business modeling.