Transitioning: matter, gender, thought takes the body, its ontologies and temporalities, as a primary ethnographic heuristic to explore transition contexts, relations and life processes. Although in Britain the Gender Recognition Act has, since 2004, provided a framework for identity recognition for those who seek to live as a member of the opposite gender, this book draws on trans men's experiences to conceptualise transition outside this framework. Thinking through changing materialities, cultures and epistemologies of transition, the book brings together perspectives in anthropology, transgender studies, and social theory to think through how bodies happen, and the scales, assemblages, transmissions and indeterminacies in their process of becoming something other than themselves.