In this paper we consider the problem of key management in a highly-mobile wireless networking environment, such as a dynamic, distributed setting in which command and control nodes move along with individual users. In this scenario, data must be securely multicast from one source to many users, requiring that users be properly keyed. Furthermore, because users move in and out of the session (due to mobility, attrition, and reinforcement), in order to preserve confidentiality, it becomes necessary to rekey each time a user enters or leaves. We present a hierarchical framework and key distribution algorithms for such a dynamic environment, with a focus on how keys and trust relationships are transferred when users move between so-called "areas" in the hierarchy. We present several schemes including one that rekeys every time a member moves from area to area and one that delays rekeying so long as security is not compromised. Our preliminary analytical and simulation results indicate that it is possible to trade off communication throughput with computational and security overheads. We also briefly describe a prototype testbed in which we are implementing and experimenting with these algorithms.