The concept of social capital advocates that the goodwill available from relations is a valuable resource that can facilitate collective actions. Although social capital has recently gained momentum in the buyer-supplier relationship (BSR) literature, there is a surprising lack of consensus about its antecedents, benefits, risks, and boundary conditions in such relationships. To address this void, a systematic literature review of seventy articles published in peer-reviewed journals between 2002 and 2018 was undertaken. The review identified and discusses two types of antecedents that can give rise to social capital in BSRs, namely intrafirm-level and relationship-level antecedents (i.e., structural and relational). It reveals that social capital can lead to a variety of benefits, in the form of direct performance improvements (e.g., operational) and relationship benefits (e.g., knowledge sharing), however that these benefits may vary depending on a number of boundary conditions in BSRs (e.g., contract specificity). The review also highlights that although social capital can generate benefits, it can also lead to risks that can undermine the performance and evolution of BSRs (e.g., reduced exploratory learning), suggesting a 'double-edged sword' effect. The paper concludes by summarizing current research gaps and outlining promising directions for future research.