Personality-relationship transactions were investigated in a general population sample of young German adults with three assessments over 8 years. Four general findings were obtained. First, personality development was characterized by substantive individual differences in change. Second, bivariate latent growth models indicated that individual differences in personality change were substantially associated with change in peer and family relationships. Third, forming a partner relationship for the first time moderated the maturation of personality. This finding was replicated over two subsequent time intervals with independent subgroups. Fourth, higher neuroticism and higher sociability predicted which of the singles began a partner relationship during the next 8 years. The results confirm that individual differences in personality development predict and result from life transitions and relationship experiences.