Why states act through formal international organizations

States use formal international organizations (IOs) to manage both their everyday interactions and more dramatic episodes, including international conflicts. Yet, contemporary international theory does not explain the existence or form of IOs. This article addresses the question of why states use formal organizations by investigating the functions IOs perform and the properties that enable them to perform those functions. Starting with a rational-institutionalist perspective that sees IOs as enabling states to achieve their ends, the authors examine power and distributive questions and the role of IOs in creating norms and understanding. Centralization and independence are identified as the key properties of formal organizations, and their importance is illustrated with a wide array of examples. IOs as community representatives further allow states to create and implement community values and enforce international commitments.