In this thesis, we propose an adaptive multicast key management scheme for secure group communications. In a secure communication session, group members could dynamically join and leave the group. Therefore, a multicast key management scheme is required to ensure that only legitimate users will continue to receive the latest information. In the literature, star-based key management schemes and tree-based key management schemes were proposed for secure group communications. In this thesis, we propose a novel canonical-tree-based key management scheme. We evaluate the average rekeying costs of the canonical-tree-based scheme as well as two well-known key management schemes. We find that the leaving probability of group members dominates the relative performance between the star-based scheme and the tree-based scheme. Based on the above observations, we propose an adaptive key management scheme that is superior to both the star-based scheme and the tree-based scheme in a dynamic environment.