Generic drugs cannot be marketed without regulatory and clinical demonstration of "bioequivalence." The authors argue that the concept of "bioequivalence" is a joint regulatory and scientific creation, not purely a technical concept, and not purely a legal concept. It developed at the interstices of networks of pharmacologists, regulators, food and drug lawyers, and American and European policy makers interested in "generic" drugs. This article provides a situated perspective on the history of bioequivalence, which emphasizes the shaping role of the state upon scientific processes, networks of regulators and scientists, and the centrality of transnational dynamics in the formation of drug regulatory standards.