This paper addresses the problem of specifying and establishing secure collaborations between autonomous entities that need to interact and depend on each other in order to accomplish their goals. We call such collaborations missionoriented dynamic communities. We propose an abstract model for policy-based collaboration that relies on a set of task-oriented roles. Nodes are discovered dynamically and assigned to one or more roles, and then start enforcing the policies associated with these roles according to the description of the community. In this paper we describe a basic set of management roles that are needed to provide management and security functions for dynamic communities. Policies are used to specify management protocols as these can be easily modified to reflect different adaptive strategies. We focus on collaboration between nodes in the context of mobile ad-hoc networks. Our implementation is based on a surveillance scenario using unmanned autonomous vehicles (UAVs). However our approach to dynamic communities could be applied to emergency services at a disaster site, search and rescue applications or many military scenarios.