We introduce Adaptive Smooth Simulcast Protocol (ASSP) for simulcast transmission over best-effort networks. ASSP is a new multiple-rate protocol that implements a single rate TCP-friendly protocol as the underlying congestion control mechanism for each simulcast stream. ASSP is build on top of the RTP/RTCP protocol and exploits the RTCP sender and receiver reports for the dissemination of feedback information. The key attributes of ASSP are: a) TCPfriendly behavior, b) adaptive per-stream transmission rates, c) adaptive scalability to large sets of receivers and finally d) smooth transmission rates that are suitable for multimedia applications. We evaluate the performance of ASSP and investigate its behavior through simulations conducted with the network simulator software (ns2).