Throughout our lives periods of change and transition are inevitable, whether it is starting school, taking up employment, moving house, having children, retiring, or moving into care. Some transitions are planned and some unexpected, but all are associated with varying degrees of uncertainty; even those that change our lives for the better. How we manage that uncertainty is key to protecting well-being and ensuring successful transition, and this, we argue, has its basis in the availability of strong supportive networks of relationships with others, particularly groups of others. It is from these relationships that we gain the support required to manage and adjust to change, and this is even more vital when that change is especially challenging, as in the case of recovery from addiction. As we will argue, the challenge in this life transition lies in engineering the process of social identity change – one that involves moving away from drug using networks to sustained engagement with networks supportive of recovery. Social identity theorizing provides a framework to understand the role that social identities play in this transition and a basis from which to map their influence. In this chapter, we outline a theoretical framework that explains adjustment to social identity change and introduce the Social Identity Mapping (SIM) tool to measure such change in the process of recovery.