This study untangles the social processes and inter-firm mechanisms underlying human resource management (HRM) knowledge networks. The research questions serve to advance understanding of why HRM knowledge flows between firms under contractual relationships and in the absence of formal relationships. The study analyzes data from a complete network of 51 high-technology firms located in a science and technology park to report the structural properties and relational dimensions of inter-firm flow of HRM knowledge. The results from this social network analysis show that the firms in the study actively engage in the sharing of HRM knowledge. Specifically, the results not only indicate the preeminence of formal ties but also of relational factors relating to firm legitimacy, prestige, and collaborative interaction. Participation in inter-firm knowledge networks appears to be an effective tool for obtaining HRM knowledge as well as for enhancing legitimacy and prestige between firms and developing trust and reciprocity within collaborative relationships.