The chapter discusses the book "Explaining Institutional Change: Ambiguity, Agency and Power," edited by James Mahoney and Kathleen Thelen, which revisits and expands upon the study of institutions. The book critiques the common view that institutional change occurs only during brief periods of intense transformation, arguing instead that change is often gradual and continuous. Thelen's critique of the interrupted equilibrium theory highlights how small, gradual changes can lead to adaptation and evolution through reconfigurations in the coalitions that support institutions. The book presents a detailed and consistent theory of gradual change, identifying three key ingredients: the ambiguity in rules, agents willing to exploit this ambiguity, and competition among these agents. The form of change depends on the interaction between political context, institutional characteristics, and dominant agent types. The authors propose four modalities of gradual change: displacement, addition, conversion, and drift. The book also explores various typologies of change agents and their alliances, showing how different types of agents can alter the future of institutions. The richness of the theoretical model is demonstrated through diverse case studies, such as the Brazilian public health system, which institutionalized practices from the dictatorship era, and the Kenyan land documentation system, which was undermined by parasitic agents. The chapter also discusses the American social security system, which is seen as a programmatic institution that has survived through constant, gradual change driven by conflict among conservative fiscal activists, left-wing expansionists, and orthodox right-wing conservatives. The book concludes by emphasizing the importance of ambiguity, agency, and power in understanding institutional change, aligning with Elinor Ostrom's call for a more nuanced and realistic approach to institutional study.The chapter discusses the book "Explaining Institutional Change: Ambiguity, Agency and Power," edited by James Mahoney and Kathleen Thelen, which revisits and expands upon the study of institutions. The book critiques the common view that institutional change occurs only during brief periods of intense transformation, arguing instead that change is often gradual and continuous. Thelen's critique of the interrupted equilibrium theory highlights how small, gradual changes can lead to adaptation and evolution through reconfigurations in the coalitions that support institutions. The book presents a detailed and consistent theory of gradual change, identifying three key ingredients: the ambiguity in rules, agents willing to exploit this ambiguity, and competition among these agents. The form of change depends on the interaction between political context, institutional characteristics, and dominant agent types. The authors propose four modalities of gradual change: displacement, addition, conversion, and drift. The book also explores various typologies of change agents and their alliances, showing how different types of agents can alter the future of institutions. The richness of the theoretical model is demonstrated through diverse case studies, such as the Brazilian public health system, which institutionalized practices from the dictatorship era, and the Kenyan land documentation system, which was undermined by parasitic agents. The chapter also discusses the American social security system, which is seen as a programmatic institution that has survived through constant, gradual change driven by conflict among conservative fiscal activists, left-wing expansionists, and orthodox right-wing conservatives. The book concludes by emphasizing the importance of ambiguity, agency, and power in understanding institutional change, aligning with Elinor Ostrom's call for a more nuanced and realistic approach to institutional study.