Social factors are major determinants of the success of retirement transitions. However, we do not yet fully understand the nature and basis of this impact, particularly as it relates to social group belonging. To address this issue the present article investigated the role that social group memberships play in supporting people's health and well-being in the early phase of transitioning to retirement. More specifically, we drew on the social identity model of identity change (SIMIC) to examine two pathways in which social group processes are theorized to influence adjustment to life change-social identity continuity and social identity gain. To test these pathways, a sample of Australian workers who had transitioned to retirement in the last 12 months (N = 170) were surveyed about their (a) preretirement multiple group memberships and postretirement maintained and new group memberships and (b) their perceived physical health, mental health, and life satisfaction after retirement. While preretirement group memberships did not affect retirement outcomes directly, they supported them indirectly by enabling people both to maintain some existing group memberships and to gain some new group memberships postretirement; as predicted by SIMIC. These findings confirm the importance of social factors and of social group membership in particular, for retiree health and well-being. Theoretically, they support the generalizability of SIMIC and its capacity to explain adjustment to diverse life changes including retirement. (PsycInfo Database Record (c) 2023 APA, all rights reserved).