Starting with the imminent roll-out of the IP Multimedia Subsystem (IMS) and fourth-Generation networking technology, Next Generation Networks (NGN) are gradually becoming reality, with charging and Quality-of-Service (QoS) issues as two of the key drivers for the evolution toward 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—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 communication services, the emergence of viable business models, pricing schemes, and charging and accounting mechanisms is of paramount importance. Problems in this domain can only be addressed through a broad interdisciplinary approach linking together a variety of technical and economic perspectives, which are constantly driving a plethora of relevant research t- ics for application developers, business architects, network providers, service providers, and customers. Within the current trend toward a convergent NGN architecture, compe- tion modeling, pricing mechanisms, and the economics of inter-domain traffic are of specific importance and urgency. Thus, they determined—in the form of three technical sessions—the core of the ICQT 2009 program.