This book investigates the specific conception and descent of a language of "degeneration" from 1848 to 1918, with particular reference to France, Italy, and England. The author shows how in the refraction and wake of evolution and naturalism, new images and theories of atavism, "dégénérescence" and socio-biological decline emerged in European culture and politics. He indicates the wide cultural and political importance of the idea of degeneration, while showing that the notion could mean different things at different times in different places. Exploring the distinctive historical and discursive contexts in France, Italy, and England within which the idea was developed, the book traces the profound complex of political issues to which the concept of degeneration gave rise during the period from the revolutions of 1848 to the First World War and beyond.