How has populism transformed party systems in Europe? I survey the varieties of populism, the sources of their support and the different ways that they appeal to voters. I use data from the Chapel Hill Expert Survey to explore whether populist parties are intensifying competition on the cultural dimension, accelerating the decline of mainstream parties, and increasing polarization. I argue that while left and center populist parties have upended existing structures of competition, it is longstanding conservative parties, remodeled using ethnopopulism, that have been the most consequential for the substance of political competition and the trajectory of domestic politics. I consider the behavior of incumbents and argue that varieties of populism should shape our expectations of what happens when populists rule: While left populist parties in power over the last decade have tended to become more ordinary, sometimes even shedding antiestablishment and anti-EU positions, ethnopopulist parties in power have used harsh “us-versus-them” appeals, misinformation, and democratic backsliding in their pursuit of more power. Expected final online publication date for the Annual Review of Political Science, Volume 24 is May 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.