As the post-WWII liberal democratic consensus comes under increasing assault around the globe, Zachary R. Goldsmith investigates a timely topic: the reemergence of fanaticism. His book demonstrates how the concept of fanaticism, so often flippantly invoked with little forethought, actually has a long history stretching back to ancient times. Tracing this history through the Reformation and the Enlightenment to our present moment of political extremism run amok, Goldsmith offers a novel account of fanaticism, detailing its transformation from a primarily religious to a political concept around the time of the French Revolution. He draws on the work of Immanuel Kant, Edmund Burke, and Fyodor Dostoevsky—all keen observers of fanaticism, and especially its political variant—in order to explore this crucial moment in the development of political fanaticism. Examining conceptualizations of fanaticism from different geographical, political, temporal, and contextual backgrounds, Goldsmith reveals how the concept has changed over time and resists easy definition. Nevertheless, his analysis of the writings of key figures from the tradition of political thought regarding fanaticism yields a complex and nuanced understanding of the concept that allows us to productively identify and observe its most salient characteristics: irrationality, messianism, the embrace of abstraction, the desire for novelty, the pursuit of perfection, a lack of limits in politics, the embrace of violence, certainty, passion, and its perennial attraction to intellectuals. Goldsmith’s political-philosophical history of fanaticism offers us an argument and warning against fanaticism itself, demonstrating that fanaticism is antidemocratic, illiberal, antipolitical, and never necessary.