In this paper, we propose an energy-efficient on-demand multicast routing protocol (EMP) for wireless ad hoc and sensor networks. The design objective is to prolong the network lifetime of such networks. For this purpose, EMP introduces the strategy of energy critical avoidance in the process of ondemand construction of multicast routing trees. That is, those energy-critical nodes in the network are discouraged from in-volving a multicasting task. EMP also incorporates the destination-driven feature in its tree construction process in order to reduce the tree cost. We present the detailed design description of EMP. Simulation results show that EMP can achieve high performance in terms of network lifetime.