Multicast is an efficient mechanism to transmit data to multiple receivers in wireless networks. In this paper, we explore rate optimization for multicast communications at the media access control (MAC) layer in wireless networks. We first consider network models with single-input-single-output (SISO) links. For threshold-based multicast policies, we characterize the optimal transmission rates that maximize the throughput in stable networks and in saturated networks, respectively. We then investigate the tradeoff between stability and throughput therein. Furthermore, we generalize our study to networks with multipleinput-multiple-output (MIMO) links and non-i.i.d. channel links, and investigate the optimal transmission rate correspondingly.