Guided by a grounded theory methodology, the authors propose a theory of rehabilitation for incarcerated persons within a prison equine program (PEP). Interviews with ten incarcerated men yielded a grounded theory of rehabilitative change centered around the importance of relationships with program staff and horses, and the uniqueness of the barn-equine environment in promoting safe attachments and positive views of self. Special emphasis is placed on the development of secure reparative attachments between men and their horses grounded in acceptance and mutual empathy, as well as the development of redemptive identities whereby participants viewed themselves as having purpose and value as human beings. Implications for policy and practice for fostering effective rehabilitation in incarceration settings are discussed.