In this introductory chapter, we outline the book's general argument on policy accumulation and the democratic responsiveness trap. We argue that in democracies, legitimacy emerges through the political system's responsiveness to societal demands. However, democratic responsiveness also entails policy accumulation, i.e. the continuous addition of new policy elements to existing policy mixes. While policy accumulation reflects modernization and human progress, it also undermines democratic legitimacy by lowering the quality of policy debates, impairing implementation efforts and complicating policy evaluation. Therefore, policy makers are stuck in a responsiveness trap: being unresponsive will undermine their legitimacy, while being responsive—and thereby accumulating policies and regulations—will slowly and silently overburden the administrative, evaluative, and communicative capacities that help support the legitimacy of democratic government in the long run. While we share the notion of recent contributions that populism presents a real threat to the sustainability of democratic government, we add that policy accumulation provides fertile ground for populist movements.