Moral injury (MI), originally discussed in relationship to transgressing moral beliefs and values during wartime among military personnel, has expanded beyond this context to include similar emotions experienced by healthcare professionals, first responders, and others experiencing moral emotions resulting from actions taken or observations made during traumatic events or circumstances. In this article, we review the history, definition, measurement, prevalence, distinctiveness, psychological consequences, manifestations (in and outside of military settings), and correlates of MI in different settings. We also review secular psychological treatments, spiritually integrated therapies, and pastoral care approaches (specific for clergy and chaplains) used to treat MI and the evidence documenting their efficacy. Finally, we examine directions for future research needed to fill the many gaps in our knowledge about MI, how it develops, and how to help those suffering from it.