- In this paper, we present a framework for resource allocations for multicast device-to-device (D2D) communications underlaying a cellular network. The objective is to maximize the sum throughput of active cellular users (CUs) and feasible D2D groups in a cell, while meeting a certain signal-to-interferenceplus- noise ratio (SINR) constraint for both the CUs and D2D groups. We formulate the problem of power and channel allocation as a mixed integer nonlinear programming (MINLP) problem where one D2D group can reuse the channels of multiple CUs and the channel of each CU can be reused by multiple D2D groups. Distinct from existing approaches in the literature, our formulation and solution methods provide an effective and flexible means to utilize radio resources in cellular networks and share them with multicast groups without causing harmful interference to each other. A variant of the generalized bender decomposition (GBD) is applied to optimally solve the MINLP problem. A greedy algorithm and a low-complexity heuristic solution are then devised. The performance of all schemes is evaluated through extensive simulations. Numerical results demonstrate that the proposed greedy algorithm can achieve closeto- optimal performance, and the heuristic algorithm provides good performance, though inferior than that of the greedy, with much lower complexity.