A moral injury is an injury to an individual's moral conscience and values resulting from an act of perceived moral transgression on the part of themselves or others. It produces profound feelings of guilt or shame, moral disorientation, and societal alienation. In some cases it may cause a sense of betrayal and anger toward colleagues, commanders, the organization, politics, or society at large.

Moral injury is most often studied in the context of military personnel, and is studied in occupational groups that frequently encounter "high-stakes" situations. It has been studied in healthcare workers (especially during the COVID-19 pandemic), prison officers, humanitarian aid workers, human trafficking survivors, people involved in accidents, and people who have been raped or abused.

Psychiatrist Jonathan Shay and colleagues coined the term moral injury to describe experiences where someone who holds legitimate authority has betrayed what is morally right in a high-stakes situation. The concept of moral injury emphasizes the psychological, social, cultural, and spiritual aspects of trauma.

According to the International Centre for Moral Injury, it "involves a profound sense of broken trust in ourselves, our leaders, governments and institutions to act in just and morally 'good' ways" and the experience of "sustained and enduring negative moral emotions - guilt, shame, contempt and anger - that results from the betrayal, violation or suppression of deeply held or shared moral values."

The US Department of Veterans Affairs uses the term moral injury to describe the experiences of military veterans who have witnessed or perpetrated actions in combat that transgressed their deeply held moral beliefs and expectations.

In 1984, the term moral distress was first conceptualized by philosopher Andrew Jameton in his book on nursing issues, Nursing Practice: The Ethical Issues to describe the psychological conflict nurses experienced during "ethical dilemmas". He wrote that "moral distress arises when one knows the right thing to do, but institutional constraints make it nearly impossible to pursue the right course of action."

In the 1990s, the term moral injury was coined by psychiatrist Jonathan Shay and colleagues based upon numerous narratives presented by military/veteran patients given their perception of injustice as a result of leadership malpractice. Shay's definition of moral injury had three components: 'Moral injury is present when (i) there has been a betrayal of what is morally right, (ii) by someone who holds legitimate authority and (iii) in a high-stakes situation. As of 2002, Shay defined moral injury as stemming from the "betrayal of 'what's right' in a high-stakes situation by someone who holds power."

In 2009, the term moral injury was modified by Brett Litz and colleagues as "perpetrating, failing to prevent, or bearing witness to acts that transgress deeply held moral beliefs and expectations may be deleterious in the long term, emotionally, psychologically, behaviorally, spiritually, and socially" (2009, p. 695). According to Litz et al., the term moral injury had been developed in response to the inadequacy of mental health diagnoses, such as post-traumatic stress disorder (PTSD), to encapsulate the moral anguish service members were experiencing after returning home from war. Unlike PTSD's focus on fear-related symptoms, moral injury focuses on symptoms related to guilt, shame, anger, and disgust. The shame that many individuals face as a result of moral injury may predict symptoms of posttraumatic stress disorder.