Many individuals use self-help groups and other forms of group therapy to achieve and maintain cessation from addictive behaviours. For instance, self-help group attendance has been shown to improve outcomes in a variety of studies (Kelly, Stout, Magill, Tonigan, & Pagano, 2012; Blonigen, Timko, Finney, Moos, & Moos, 2011; Kelly, Hoeppner, Stout, & Pagano, 2010). They are also popular – some estimates suggest that 80 per cent of US drinkers who are trying to cease alcohol use will attend Alcoholics Anonymous at some point (Dawson, Grant, Stinson, & Chou, 2006). In formal treatment settings such as residential treatments and thera - peutic communities, some form of group therapy is an almost ubiquitous feature of the treatment regime. The current chapter suggests that the efficacy of such treatment modes can be understood in part by understanding the social identities (those identities which are associated with social groupings, see Tajfel, 1978 and Tajfel & Turner 1979) that develop around addiction – both those focused on addiction (‘alcoholic’, ‘gambler’) and those focused on cessation (‘recovering addict’, ‘former gambler’). How these identities operate is described in the Social Identity Model of Cessation Maintenance (SIMCM, Frings & Albery, 2015) the mechanisms and implication of which are explored in the current chapter.