Many networked multimedia applications are delay-sensitive, and hence desire services with guarantees of resouce availability and timeliness. For networks such as those based on Asynchronous Transfer Mode (ATM), these services are specified through Quality of Service (QoS) parameters. Delivering end-to-end QoS implies complex resource management at the end-points (e.g., computer workstation hosts), as well as in the underlying network. In this paper, we describe a model for an end-point entity, which we have designed and implemented, called the QoS Broker. The broker orchestrates resources at the end-points, cooperating with resource management in the underlying ATM network. The broker, as an intermediary, hides implementation details from applications and resource managers. We motivate the concept and particulars of our design, including services such as translation, admission and negotiation which the broker uses to properly configure the system to application needs. We treat the QoS negotiation as a 'deal' between the user ("buyer") and the network ("seller") for the setup of a customized connection. The key concept is that the broker is an active intermediary which isolates cooperating entities from operational details of other entities.