Starting with the imminent roll-out of the IP Multimedia Subsystem (IMS) and fourth-generation networking technology, Next Generation Networks (NGN) are gradually becoming a reality, with charging and quality-of-service (QoS) issues as two of the key drivers for the evolution towards the convergent all-IP network of the future. Therefore, the 6th International Workshop on Internet Charging and QoS Technology (ICQT 2009) was devoted to discussing the most recent approaches, models, and mechanisms in this highly interesting and important research area. The present volume of the Lecture Notes in Computer Science series includes those papers presented at ICQT 2009, which was collocated this year with the IFIP Networking 2009 conference, taking place on May 15, 2009, in Aachen, Germany and hosted by the Rheinisch-Westfälische Technische Hochschule (RWTH Aachen). For the commercial success of future QoS-enabled.