Radical-right behavior is increasing across Western democracies, often very fast. Previous research has shown, however, that political attitudes and preferences do not change this fast. This book argues that, to understand these patterns, one needs to appreciate the crucial role of social norms as drivers of political behavior. It builds on a norms-based theory of political supply and demand, arguing that growing radical-right behavior is driven by individuals who already held radical-right views, but who did not act on them because they thought that they were socially unacceptable. If these voters do not express their preferences, politicians can underestimate how much latent support there is for radical-right policy. This leaves the radical right with less skilled leaders, who are unable to mobilize even radical-right voters to support them. However, if politicians realize that there is more private support for radical-right policy than is typically observable, they have an incentive to run for election on a radical-right platform and mobilize silent radical-right views. Their electoral success, in turn, makes radical-right individuals become more comfortable showing their views, and impels more politicians to join the radical right. The argument of the book makes us rethink how political preferences translate into behavior, shows how social norms affect the interaction of political supply and demand, and highlights how a political culture that promotes inclusion can erode.