This Element provides a critical review of existing literature on the role of ideas and institutions in the politics of public policy with the aim of contributing to the study of the politics of public policy. Because most policy scholars deal with the role of ideas or institutions in their research, such a critical review should help them improve their knowledge of crucial analytical issues in policy and political analysis. The following discussion brings together insights from both the policy studies literature and new institutionalism in sociology and political science, and stresses the explanatory role of ideas and institutions.