This article addresses the following question: Under what conditions, in what ways, and to what degree should various strands of theorizing at the international level — structural realism, institutionalism, constructivism — incorporate various categories of psychological theory? The article samples the diverse ways in which such interweaving of levels of analysis has either already begun or could be readily initiated given recent empirical and theoretical developments. The most promising candidates for conceptual integration are organized into four broad categories which identify: the appropriate boundary conditions for the applicability of clashing hypotheses within the structural-realist tradition; the factors that facilitate and impede the creation of international institutions and norm enforcement mechanisms within the institutionalist tradition; the factors that determine whether policy-makers and epistemic communities frame issues in terms of the logic of consequential action or the logic of obligatory action within the constructivist tradition; and the price that international relations theorists pay for placing a hedgehog-style premium on theoretical parsimony and the value of adopting a more flexible, foxlike, contextualist style in future theory-building exercises.