Professionals in healthcare are increasingly encouraged to work together. This has acted as a catalyst for research on interprofessional collaboration. Authors suggest developing interprofessional collaboration is not just the job of managers and policy makers; it also requires active contributions of professionals. Empirical understanding of whether professionals make such contributions and if so, how and why, remains fragmented. This systematic review of 64 studies from the past 20 years shows there is considerable evidence for professionals actively contributing to interprofessional collaboration. Although the evidence is limited, we can show they do so in three distinct ways: by bridging professional, social, physical and task-related gaps, by negotiating overlaps in roles and tasks, and by creating spaces to be able to do so. Professionals from different professions seem to make different contributions. Moreover, differences exist between collaborative settings and healthcare subsectors. We conclude by proposing a research agenda to advance our understanding of these contributions in theoretical, methodological and empirical ways.