The present study examined the influence of stable personality traits on romantic relationships using longitudinal data on a large, representative sample of young adults. Relationship experiences (quality, conflict, and abuse) showed relatively small mean-level changes over time and significant levels of rank-order stability, even across different relationship partners. Antecedent personality traits (assessed at age 18) predicted relationship experiences at age 26 and change in relationship experiences from age 21 to 26. Conversely, relationship experiences also predicted change in personality. Importantly, these findings generally held across relationship partners, suggesting that some people tend to be generally happy (or unhappy) across relationships, and this is due, in part, to stable individual differences in personality. Discussion focuses on the broader implications of the findings, in particular the need for relationship researchers to consider the importance of personality for why relationships thrive or fail and the need for personality researchers to consider the impact of relationship experiences on intraindividual personality development.