Context-awareness in dynamic and unpredictable environments is a well-studied problem, and many approaches handle sensing, understanding, and acting upon context information. Entities in these environments are not in isolation, and oftentimes the manner in which entities coordinate depends on some (implicit) notion of their shared context. In this paper, we are motivated by the need to explicitly construct notions of the context of a group that can support better coordination within the group. First we identify an efficient representation of context (both of an individual and of a group) that can be shared across wireless connections without incurring a significant communication overhead. Second we provide precise semantics for different types of groups, each with compelling use cases in these dynamic computing environments. Finally, we define and demonstrate protocols for efficiently computing groups and their context in a distributed manner.