How challenger parties, acting as political entrepreneurs, are changing European democraciesChallenger parties are on the rise in Europe, exemplified by the likes of Podemos in Spain, the National Rally in France, the Alternative for Germany, or the Brexit Party in Great Britain. Like disruptive entrepreneurs, these parties offer new policies a "Catherine de Vries and Sara Hobolt are arguably among the most influential scholars working on party competition in Europe. . . . Their book presents an exceptional contribution to research on European party competition that will unquestionably be a focal point of reference for any future research in this field."---Julia Schulte-Cloos, Acta Politica