This book argues that the Russian thinker Petr Kropotkin’s anarchism was a bio-political revolutionary project. It shows how Kropotkin drew on late nineteenth- and early twentieth-century European and Russian bio-social-medical scientific thought to the extent that ideas about health, sickness, insanity, degeneration, and hygiene were for him not metaphors but rather key political concerns. It goes on to discuss how for Kropotkin's bio-political anarchism, the state, capitalism, and revolution were medical concerns whose effects on the individual and society were measurable by social statistics and explainable by bio-social-medical knowledge. Overall, the book provides a refreshing, innovative approach to understanding Kropotkin’s anarchism.