The study of regimes has focused on the negotiation of rules that, in practice, have been codified into single agreements. Scholars have generally assumed that individual regimes are decomposable from others. Given the rising density of international institutions, we suggest that an increasingly common phenomenon is the "regime complex"-a collective of partially-overlapping regimes. We suggest that regime complexes evolve in special ways. They are laden with legal inconsistencies because the rules in one regime are rarely negotiated in the same fora and with the same interest groups as rules in other regimes. These inconsistencies, which occur at the joints between regimes, focus a process of problem-solving as actors attempt to resolve inconsistencies through the process of implementation; in turn, viable solutions focus later rounds of formal rule-making and legalization. We illustrate the concept of regime complexes using the rarely studied issue of property rights in plant genetic resources (PGR). Over the last century governments have created property rights in these resources in a Demsetzian process: as new technologies and ideas have made PGR more valuable, property rights have allowed firms and governments to appropriate that value. We explore our conjectures about the development of rules in a regime complex through the PGR case.