This essay introduces the two "new institutionalist" approaches to the study of law and the courts and examines some tensions between them and their combined value for enhancing our understanding of the legal matters. Behavioralism and its immediate legacies have dominated the study of the law and the courts in political science for the past four decades, and its lessons remain the starting point for any empirical examination of public law in the discipline. In different ways, the two new institutionalisms both react against this behavioralist legacy and points toward the importance of rules, norms and social practices in shaping individual behavior. The article pursues critical examination of the tensions between them and their respective limitations, as well as their potential contributions to the empirical study of the courts. The article also considers the implications of the new institutionalism for thinking about the law. Although an institutionalist perspective is useful for advancing our understanding of judicial decision-making, the real promise of this approach may be its ability to push political scientists beyond such questions. Just as behavioralism brought new subjects and questions to the field as well as new methods and assumptions, so the new institutionalism will come into its own if it succeeds in changing the research agenda and directing political scientists to look beyond the voting behavior of justices.