Despite a growing interest in how group membership can positively impact health, little research has addressed directly the role social identity processes can have on recovery from addiction. Drawing on social identity theory and self-categorization theory, the present study investigated how recovery group membership can introduce a new social identity associated with recovery, compared to the social identity associated with addiction. We hypothesized that two processes--evaluative differentiation and identity preference--would be linked with higher self-efficacy and positive health outcomes (i.e., reduced relapse, lower levels of appetitive behavior, and elevated feelings of social connectedness [Study 2]). Study 1 recruited members (N = 61) from United Kingdom based mutual aid groups of Alcoholics Anonymous and Narcotics Anonymous. Study 2 recruited ex-smokers (N = 81) from online sources. In Study 1, evaluative differentiation was significantly related to lowered relapse and reduced appetitive behavior. Identity preference was related to higher levels of self-efficacy, which was related to months drug-free and reduced levels of appetitive behaviors. In Study 2, evaluative differentiation was related to identity preference. Identity preference was also related to higher self-efficacy, which in turn was related to lower relapse. Although exploratory, these results suggest that developing a social identity as a "recovering addict" or an "ex-smoker" and subsequently highlighting the difference between such identities may be a useful strategy for reducing relapse among people with problems associated with addictive behaviors.