Plain English Summary According to our review of the literature, the social capital that comes from networks of family relationships is both a key advantage and a potential disadvantage of family firms. The relationships among family members enable the development and sharing of experiential knowledge, strengthen communications and trust, and provide access to human, physical, and financial resources. However, when taken to excess, these relationships can deny family members in the firm access to external knowledge and resources as well as lead to entrenchment and narrow strategic thinking. In this review, we discuss how these aspects of social networks and social capital influence entrepreneurial activities, firm governance and strategy, organizational decision-making, and firm growth. Although studies of social networks in family businesses have proliferated into a sizable literature, the research remains fragmented into disparate strands that lack theoretical coherence. By applying an inductive coding process to 69 articles published in 29 high-impact journals from 1988 to 2020, this review summarizes, synthesizes, and highlights the contributions of social network studies to family business research. Drawing on these results, the review specifically identifies prevailing themes in the literature and outlines a platform for future research. Furthermore, this paper discusses the most important theoretical mechanisms underpinning the connection between heterogeneous family and non-family network ties and family firm outcomes. Overall, it is observed that network structure, social capital, and family firm-specific network content act as key mechanisms linking family firm networks to performance outcomes.