Multicast video streaming over multirate wireless LANs imposes strong demands on video codecs and the under-lying network. It is not sufficient that only the video codec or only the underlying protocols adapt to changes in the wireless link quality. Research efforts should be applied in both and in a synchronized way. Cross layer design is a new paradigm that addresses this challenge by optimizing communication network architectures across traditional layer boundaries. In this paper we present a cross-layer architecture for adaptive video multicast streaming over multirate wireless LANs where layer-specific information is passed in both directions, top-down and bottom-up. We jointly consider three layers of the protocol stack: the application, data link and physical layers. We analyze the performance of the proposed architecture and extensively evaluate it via simulations. Our results show that the real-time video quality of the overall system can be greatly improved by cross-layer signaling. © 2007 IEEE.