This study examines the development and ongoing activities of a collaboration between an urban elementary school and a nearby aquarium. Although the benefits of such collaborations in support of science education are touted by numerous national organizations, the pathway to creating a successful relationship between these two different institutions, with inherently different cultures, is less well documented. Using the theoretical framework of communities of practice (E. Wenger, 1998), a better understanding of the challenges and successes of this collaboration is presented. In particular, the analysis suggests that participant engagement in both communities (school and aquarium) led to the development of an "overlap" in these communities of practice. This resulted when common forms of "mutual engagement," "joint enterprise," and "shared repertoire" emerged over the course of the project. Consistent with Wenger's framework, "boundary objects" and "brokers" could be identified that helped secure such overlap in this particular case. Implications of this theoretical perspective for facilitating the development of such institutional collaborations are also discussed. (Contains 2 tables.)