In the U.S. legal system, mitigation (known also as mitigating evidence or mitigating factors) encompasses facts about a defendant’s background, character, and the circumstances of the offense. While not introduced to lessen legal culpability, mitigating factors may lessen a defendant’s moral culpability. Thus, mitigation is not introduced to absolve guilt but rather to lessen a sentence or judgment by contextualizing the defendant’s behavior. Although sometimes observed in civil cases and criminal sentencing generally, the majority of mitigation is presented by criminal defense in capital (i.e., death penalty) cases. This entry describes the legal roots, definition, and practice of mitigation, concluding with a discussion of research on mitigation in capital jury decision-making.