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.