Do formal legal institutions complement or substitute social network mechanisms of knowledge protection? We explore how the composition and structure of firms’ international alliance networks changes in response to the passage of intellectual property rights (IPR) laws in their home countries. We find that, when IPR laws are strengthened, firms form more international alliances, particularly if they operate in IP intensive industries, and do so with partners from a greater diversity of countries. The significance of status (centrality) as a predictor of international alliance formation decreased after the passage of IPR laws, in line with a substitution effect that ‘democratized’ access to the global network by increasing the participation of firms that were peripheral before the legal changes. In contrast, the closure of firms’ alliance networks increased with stronger IPR laws, in line with a complementarity effect that increased the use of social control. The increase in closure was strongest in the networks of the low status entrants into the global network. Using a difference-in-difference empirical design, we found that these changes coincided exactly with the timing of the passage of the laws across thirteen countries between 1988 and 2005. This study addresses issues of great theoretical and practical importance to the literatures on institutions, networks, and IPR.