The relevance of regional security theories has grown in the wake of the Cold War. The global system has more participants—is less Eurocentric with Third World states having greater autonomy and involvement—and clearly unipolar, shifting the locus of conflict down from the global level. A new wave of regionalist scholarship has arisen in response. This review identifies this literature’s central themes and suggested new variables. Its foundational and most contested challenge to international relations (IR) theory revolves around the autonomy of a regional level of analysis between the state and the globe. Accepting such autonomy, the literature broadly settles on three variables specific to regional structures. First, regional subsystems are porous. Intervention from above can overlay local dynamics. Second, proximity qualifies the security dilemma dramatically. Most states only threaten their neighbors, thus creating meaningful and distinct regional dynamics. Third, weak state-dominant regional complexes generate a shared internal security dilemma that trumps the external one. Regional organizations serve to repress shared centrifugal threats through pooled rather than ceded sovereignty.