Moral luck is a term that is current in the philosophical literature on ethics. It suggests a fundamental problem for moral theory. The problem is this: We tend to believe that judging a person in terms of moral responsibility or in terms of moral praise or blame should depend on that person's deliberate, freely done actions. A person should not be morally praised or blamed for things that simply happen to them, that are not under their control. In other words, luck should play no role in making such moral judgments. But it appears obvious that luck is (perhaps even typically) involved in moral evaluations. Consider two people performing similar acts, say drunk driving. One person, A, kills a person and the other, B, gets home safely. Suppose further that B got home safely due to luck; B would have killed if he or she faced circumstances like those faced by A. We would like to think that A and B are equally guilty of immoral actions, but in reality we tend to place serious moral blame (and legal blame) on A and little such blame on B. Moral luck, that is, seems to play a significant role in our moral thinking. On the other hand, luck may place a person in a situation to do tremendous good. Or luck may endow a person with an upbringing that provides the basis for virtuous action. If this is true, then people are not entirely the source of their own moral virtues or of their moral faults. These issues raise questions about moral agency. A moral agent is thought to be responsible for his or her actions. But moral luck may always play some part in determining how or why a person acts, thus apparently diminishing their moral agency. However, moral praise and blame may play an entirely different role. They may be used to guide actions or to create the conditions in which morally desired actions are more likely to be performed. Some philosophers who seriously consider moral luck are inclined to think that we are mistaken to think that full control over a situation is necessary for moral praise or for moral blame.