Moral injury (MI) is a potential clinical problem characterized by functionally impairing moral emotions, beliefs, and behaviors as well as adverse beliefs about personal or collective humanity and life’s meaning and purpose. MI can arise from personal transgressive acts or from being a victim of or bearing witness to others’ inhumanity. Despite widespread interest in MI, until recently, there was no reliable measure of MI as an outcome, and prior research has revealed little about its causes, consequences, and intervention approaches. This review provides background information on the history of MI, defines key terms, and critically reviews assessment tools. Additionally, we describe a social-functional theory of the etiology of MI and a social-functional rehabilitation approach to treatment. This treatment approach, which can be used by any clinician regardless of clinical context, employs cross-cutting change agents to promote lasting corrective and humanizing prosocial experiences, enhancing belonging through valued actions and relationships.