Military personnel serving in war are confronted with ethical and moral challenges, most of which are navigated successfully because of effective rules of engagement, training, leadership, and the purposefulness and coherence that arise in cohesive units during and after various challenges. However, even in optimal operational contexts, some combat and operational experiences can inevitably transgress deeply held beliefs that undergird a service member’s humanity. Transgressions can arise from individual acts of commission or omission, the behavior of others, or by bearing witness to intense human suffering or the grotesque aftermath of battle. An act of serious transgression that leads to serious inner conflict because the experience is at odds with core ethical and moral beliefs is called moral injury.