In this paper, we consider QoS support in the context of group communications. In particular, we present fundamental properties of QoS in group communications, which, although quite simple, have been widely overlooked and/or misunderstood. Because distributed multimedia applications require flexible QoS agreements, end-to-end QoS negotiation will play an important role. We show how such a negotiation mechanism can be designed, taking the fundamental QoS properties into account. This leads us to the design of an algorithm for QoS negotiation whose computational overhead proves to be independent of the size of the group of receivers.