Quality of Service (QoS) management becomes more and more important, especially in networks where many applications are competing for a limited number of resources. As these applications become more complex (consider e.g. multiparty multimedia applications), the number of options for QoS management increases, leading to more complex decision processes. In this paper, we propose an approach for cooperative QoS management, where application-oriented QoS agents are distributed throughout the network and the end systems, communicating with each other. This distributed management system tries to guarantee the QoS level negotiated with the users, at the same time optimizing resource usage. The advantages of distributing the management process are (i) an easier and more precise localization of the cause of QoS problems, (ii) better knowledge of local situations, (iii) a lower complexity for a single QoS agent and (iv) an increase in possible actions. We describe management procedures for QoS...