Background: A growing literature focuses on the roles of brokers, intermediaries, and boundary-spanners (BIBS) in addressing the challenges of transferring research evidence between the research and practice or policy communities. However, it is unclear how BIBS are used and defined in this work. Aims and Objectives: In this systematic review, we examined two key research questions: (1) Where, how, and when are different BIBS terms (i.e., broker, intermediary, and boundary spanner) used? and (2) Which BIBS terms get defined, and when these terms are defined, who are BIBS and what do they do? Methods: We conducted literature searches designed to capture articles on BIBS and the transfer of research evidence. We extracted information about eligible articles’ characteristics, use of BIBS terms, and definitions of BIBS terms. For all BIBS definitions extracted, we also coded who were counted as BIBS and what BIBS were described as doing. Findings: The search revealed an initial pool of 667 results, of which, 277 articles were included after screening. Although we coded 430 separate uses of BIBS terms in our review, only 37.2% of these uses (i.e., 160) provided explicit definitions. There were some consistent differences in the definition of BIBS terms. The terms, “broker” and “brokerage”, were commonly applied in the health sector to describe a person engaged in multiple functions including capacity building, dissemination, and relationship building. The term, “intermediary”, was commonly applied in the education sector to describe an organization engaged in dissemination. Finally, the terms, “boundary spanner” and “boundary spanning”, were commonly applied in the environment sector to describe people or organizations that engage in relationship building. Discussion and Conclusions: The results of this review demonstrated that it was uncommon for researchers to explicitly define BIBS terms. Additionally, when BIBS were defined, there were important (albeit implicit) distinctions between different terms. Based on these results, we identify archetypal definitions for brokers, intermediaries, and boundary spanners and offer recommendations for future research.