Over the last three decades, interdisciplinary cluster hiring programs have become popular on research university campuses as an approach to fostering interdisciplinary collaboration. These programs have not yet been rigorously evaluated across multiple institutions and multiple thematic fields. The paper reports the results of a survey of 199 cluster hires across 20 research universities, supplemented by interviews with 18 administrators and cluster leads at nine universities. Against the expectation of advocates, the survey responses indicate that cluster hire groups are often loosely organized and members do not typically spend much time collaborating with others in their group. Both the existence of common research agendas and the participation of individuals capable of translating across disciplinary languages are associated with higher levels of satisfaction with the collaborative environment of clusters, net of covariates, as are adequate lab spaces. Even if they do not typically lead to high levels of collaboration, clusters can, in the best case scenarios, help universities to align with emerging research areas in ways that departments may have difficulty doing.