Mobile tactical (military) networks have a number of concerns that distinguish them from commercial networks. Of primary concern is information security, achieved in part through message encryption using a common key. These networks are often wireless and ad hoc, that is they lack fixed infrastructure and communications are relayed in a multi-hop fashion. The mobility of the nodes leads to a highly dynamic and unpredictable network topology as well as a dynamic communication group membership. The focus of this thesis is on finding a secure and efficient solution to group key agreement in a tactical network. Existing group key establishment protocols were surveyed, but many were found inept in this setting. The best solution was the Arbitrary Topology Group Diffie Hellman (AT-GDH). However, this protocol has not been fully specified as no provisions were made for auxiliary key agreements. To complete the AT-GDH key agreement, additional protocols are presented to be performed upon group membership changes. Each protocol was evaluated in terms of efficiency and security. All agreements stemming from additions to the group membership were found to be highly efficient. However, the exponential key structure impedes the efficient removal of one or more participant's contributions.