This article examines the implications of the rising density of international institutions. Despite the rapid proliferation of institutions, scholars continue to embrace the assumption that individual regimes are decomposable from others. We contend that an increasingly common phenomenon is the regime complex: a collective of partially overlapping and nonhierarchical regimes. The evolution of regime complexes reflects the influence of legalization on world politics. Regime complexes are laden with legal inconsistencies because the rules in one regime are rarely coordinated closely with overlapping rules in related regimes. Negotiators often attempt to avoid glaring inconsistencies by adopting broad rules that allow for multiple interpretations. In turn, solutions refined through implementation of these rules focus later rounds of negotiation and legalization. We explore these processes using the issue of plant genetic resources (PGR). Over the last century, states have created property rights in these resources in a Demsetzian process: as new technologies and ideas have made PGR far more valuable, actors have mobilized and clashed over the creation of property rights that allow the appropriation of that value.