Existing overlay multicast (also called application layer multicast) protocols can be categorized into treefirst and mesh-first approaches by the type of overlay they build. These two approaches complement each other in terms of performance and scalability. In this paper, we propose and evaluate Hybrid Overlay Multicast Protocol (HOMP), which is specifically designed for low-delay, many-to-many applications with large receiver sets. HOMP constructs and maintains a hybrid overlay composed of a core mesh and many attached trees for data transmission, thus it shows some properties of both mesh-first and tree-first approaches. Our simulation results reveal that HOMP is a promising application layer overlay construction technique.