People often try to improve their interpersonal skills to satisfy romantic partners. However, when and why a partner appreciates these efforts is an important but underaddressed question. The present research explored how people's theories that interpersonal abilities are either fixed entities or can be changed incrementally affect their responses to relationship partner's efforts at self-improvement. Study 1 validated a new measure for these theories and showed that, compared to the former entity theorists, the latter incremental theorists were less likely to attribute recalled instances of partners' negative behaviors to dispositional causes and perceive these behaviors as fixed and stable. An experiment that induced these different implicit theories (Study 2) and a longitudinal study (Study 3) further demonstrated that perceptions of partners' self-improvement efforts led to greater increases in relationship security and quality among incremental than among entity theorists. How implicit theories may shape the interpersonal dynamics of self-improvement is discussed.