Since the emergence of public policy as a field of studypolicystudies in the middle of the twentieth century, a definitive challenge has been developing theoretical approaches for comparativecomparative policy processes. Such an approach would focus researchers on common questions, provide a shared vocabulary, specify similar concepts for description and explanation, and balance the need for structure in generalizing about commonalities across multiple contextscontext with the flexibility necessary for accurately depicting the particularities of a single context. This chapter provides a brief overview of such an approach with the Advocacy Coalition Framework (ACF). It covers its creation and foundation, past and recent contributions and niches, general description, three theories, boundaries of application, and major challenges and strategies for advancing knowledge about the policy process.