This experimental study (n = 115) investigates how group norms and individuals’ congruence with these norms predicted internalization (i.e., self-determination) of an illegal behavior. We manipulated ingroup norms in favor of versus against illegal downloading of software, and assessed participants’ behavioral intentions, their motivations for emitting this specific behavior, and how they subjectively experienced the experimental situation (compartmentalizing their illegal behavior; feeling conflicted). Participants were more likely to endorse the behavior that was normative in their ingroup. Also, participants were more self-determined to engage in the behavior when they intended to behave congruently with a norm against illegal downloading, and when they intended to behave incongruently with a norm in favor of illegal downloading. Participants who did not intend to engage in illegal downloading felt less compartmentalized and conflicted than participants who intended to engage in illegal downloading. Results are discussed in light of self-determination theory (Deci & Ryan, 2000) and social identity theory (Tajfel & Turner, 1986).