Immersion is about the extreme sport of marathon swimming. Drawing on extensive (auto)ethnographic data, Immersion explores the embodied and social processes of becoming a marathon swimmer and investigates how social belonging is produced and policed. Using marathon swimming as a lens, this foundation provides the basis for an exploration of what constitutes the 'good' body in contemporary neoliberal society across a range of sites including charitable swimming, fatness, gender and health. The book argues that the self-representations of marathon swimming are at odds with its lived realities, and that this reflects the entrenched and limited discursive resources available for thinking about the sporting body in the wider social and cultural context. The book is aimed primarily at readers at undergraduate level and upwards with an interest in sociology, the sociology of the body, the sociology of sport, gender and the sociology of health and illness.