Multilateralism, Bilateralism, and Unilateralism in Foreign Policy

International relations scholars have long been working on how diplomacy can be understood by distinguishing diplomatic interactions in terms of multilateralism, bilateralism, and unilateralism. The so-called quantity-based approach focuses on the numbers of countries involved. Applying this framework, multilateralism needs more than three states in interactions; bilateralism needs two states; and unilateralism can be pursued by only a single state. However, there are more quality-based approaches to distinguish these interactions. Multilateralism requires states to follow international norms and pay more respect to international institutions; this is contrasted with unilateralism, where a single state can influence how international relations can be conducted. To understand multilateralism in foreign policy, it is crucial to understand how international society has developed institutions, norms, and regimes. By contrast, studies of unilateralism and bilateralism tend to focus on how a powerful state conducts its foreign policy by neglecting international institutions and legal constraints. This article introduces some recent evidence-based research on how multilateralism, bilateralism, and unilateralism are selected in a particular foreign policy area such as alliance formation, mediation, and international aid. The article covers how scholars frame research questions in each issue area and analyzes whether there are similarities or differences in research methods, data, and theoretical frameworks.