Abstract
This chapter first explains the concept of theory and what it does. It then illustrates the formative power of theory by contrasting two very different accounts of international law: the New Haven School, which was elaborated principally by Myres McDougal and Harold Lasswell in Yale Law School; and the pre-perestroika Soviet theory of international law propounded by GI Tunkin. The chapter argues that despite their differences, the New Haven and Soviet schools share a common approach: both are instrumental theories of law, aimed at guiding and informing practice. It also considers hegemonic theory, which views international law through the prism of a variant of United States constitutional theory that is rooted in a conservative, if not libertarian, democratic doctrine.