The present research examined how actor and partner attachment insecurity relates to biases in perceptions of partners’ core relationship-relevant constructs. Across three dyadic studies (N _couples = 333, N _individuals = 666), we examined attachment anxiety and avoidance as predictors of over- or underestimation of partners’ relationship satisfaction, commitment, and responsiveness, using partners’ own reports as the reference point for evaluating bias. Actors higher in avoidance and actors with partners higher in avoidance perceived their partners to be less satisfied and committed. In addition, actors higher in avoidance and actors higher in anxiety displayed a pessimistic bias, perceiving their partners to be less satisfied and committed than their partners reported being. Finally, actors with partners higher in avoidance displayed an optimistic bias, perceiving their partners to be more satisfied and committed than their partners reported being. Results underscore the importance of adopting a dyadic perspective on perceptual biases in romantic relationships.