The social nature of crime is one of the most well-recognized and established features of offending. Accomplices come in many forms, ranging from informal co-offenders drawn from available pools of offenders (i.e., friends, acquaintances) to more formal gang-related associates. For the purposes of this review, an accomplice will be considered anyone an individual has engaged in crime or participated in a criminal enterprise with. This broad definition (as opposed to its strict legal definition) enables an exhaustive and theoretically meaningful assessment of the group nature of crime to include collective spontaneous crime, co-offending, gang-related, and organized crime. Even within various accomplice relationships, individuals occupy various roles and positions that contribute to the diffusion of information within accomplice networks, commission of crime, and consequences. The study of accomplices has led to descriptive patterns of group-based offending, theoretical development aimed at understanding the decision to engage in crime with others, and a consideration of how such involvement impacts subsequent behavior. The following entry overviews key areas related to accomplices and references scholarship that explores this important dimension of crime.