Objective This study examines the prospective and bidirectional association between personal identity processes and relationship formation using longitudinal survey data from Finland.Background Although psychological factors have increasingly been studied as determinants for family formation processes, the role of identity exploration and commitment processes for relationship formation has been underexplored. We show that identity (un)certainty in the domain of future life plans is an important driver for relationship formation, and that relationship status may shape identity (un)certainty in turn.Method We apply event-history analyses in order to study the prospective power of both separate identity processes (variable-centered approach) and clusters of these (person-oriented approach) on relationship formation risks. Furthermore, we conduct fixed effects linear regression models for examining identity development over time based on relationship status.Results Findings suggest that identity uncertainty is negatively, and certainty is positively associated with relationship formation risks over time. Results based on cluster analyses support these findings, that is, committers are more likely to enter a relationship, in particular marriage, than explorers. Mixed findings with regard to identity development over time emerge. Whereas firm identity (i.e., commitment) remains stable over time among partnered individuals, it decreases among singles. However, relationship status does not impact exploration developments.Conclusion Relationship formation decisions in contemporary Finland are intertwined with the (un)certainty of personal identity.