1 Abstract A novel and simple approach for deening end-to-end Quality of Service (QoS) in Video-on-Demand (VoD) services is presented. Using this approach we derive a schedulable region for a video server which guarantees end-to-end QoS, where a speciic QoS required in the video client translates into a QoS speciication for the video server. Our methodology is based on a generic model for VoD services which is extensible to any VoD system. In this kind of system, both the network and the video server are potential sources of QoS degradation. Speciically, we examine the eeect that impairments in the video server and video client have on the video quality perceived by the end user. The Columbia VoD testbed is presented as an example to validate the model through experimental results. Our model can be connected to network QoS admission control models to create a uniied approach for admission control of incoming video requests in the video server and network.