A new theoretical framework for understanding how social, economic, and political conflicts influence international institutions and their place in the global order Today’s liberal international institutional order is being challenged by the rising power of illiberal states and by domestic political changes inside liberal states. Against this backdrop, Ideology and International Institutions offers a broader understanding of international institutions by arguing that the politics of multilateralism has always been based on ideology and ideological divisions. Erik Voeten develops new theories and measures to make sense of past and current challenges to multilateral institutions. Voeten presents a straightforward theoretical framework that analyzes multilateral institutions as attempts by states to shift the policies of others toward their preferred ideological positions. He then measures how states have positioned themselves in global ideological conflicts during the past seventy-five years. Empirical chapters illustrate how ideological struggles shape the design of international institutions, membership in international institutions, and the critical role of multilateral institutions in militarized conflicts. Voeten also examines populism’s rise and other ideological threats to the liberal international order. Ideology and International Institutions explores the essential ways in which ideological contestation has influenced world politics.