Contemporary international relations are legalized to an impressive extent, yet international legalization displays great variety.
A few international institutions and issueareas approach the theoretical ideal of hard legalization,but most international law is
‘‘soft’’ in distinctive ways. Here we explore the reasons for the widespread legalization of international governance and for this great variety in the degrees and forms of legalization.1 We argue that international actors choose to order their relations through international law and design treaties and other legal arrangements to solve specific substantive and political problems. We further argue that international actors choose softer forms of legalized governance when those forms offer superior institutional solutions. We analyze the benefits and costs of different types of legalization and
suggest hypotheses regarding the circumstances that lead actors to select specific forms. We do not purport to develop a full theory of law. Nonetheless, examining these political choices in the spare institutional context of internationalrelations may contribute to a better understanding of the uses of law more generally.