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 bene ts 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 international relations may
contribute to a better understanding of the uses of law more generally.
We begin by examining the advantages of hard legalization.The term hard law as
used in this special issue refers to legally binding obligationsthat are precise (or can
be made precise through adjudicationor the issuance of detailed regulations) and that
delegate authority for interpreting and implementing the law.2 Although hard law is
not the typical international legal arrangement, a close look at this institutionalform
provides a baseline for understanding the bene ts and costs of all types of legalization