We live in the age of fitness. Hundreds of thousands of people run marathons and millions go jogging in local parks, work out in gyms, cycle, swim, or practice yoga. The vast majority are not engaged in competitive sport and are not trying to win any medals. They just want to get fit. Why this modern preoccupation with fitness? In this new book, Jürgen Martschukat traces the roots of our modern preoccupation with fitness back to the birth of modern societies in the eighteenth century, showing how the idea of fitness was interwoven with modernity's emphasis on perpetual optimization and renewal. But it is only in the period since the 1970s, he argues, that the age of fitness truly emerged, as part and parcel of our contemporary neoliberal era. Neoliberalism enjoins individuals to work on themselves, to cultivate themselves in body and mind. Fitness becomes a guiding principle of social life, an era-defining network of discourses and practices that shape individuals' actions and self-conceptions. The pursuit of fitness becomes a cultural repertoire that is deeply ingrained in our institutions and way of life. This wide-ranging book shows how deeply fitness is inscribed in modern societies, and how important fitness has become to success or failure, recognition or exclusion, in a society that sets great store by self-responsibility, performance, market, and competition. It will be of great value not only to those interested in sport and fitness, but also to anyone concerned with the conditions of success and failure in our societies today.