This study tested the prediction that spouses’ insecure attachment orientation would be negatively associated with relationship quality. It was further predicted that there would be indirect effects of attachment orientation on spouses’ relationship quality through interpersonal trust as well as indirect effects of attachment orientation on loneliness through spouses’ relationship quality. Predictions were tested on 225 married couples that completed measures of attachment orientation, personal commitment, dedication commitment, interpersonal trust, loneliness, and marital satisfaction. Tests of actor–partner interdependence revealed that insecure attachment (i.e., anxious and avoidant) was associated with lower relationship quality and that one partner’s insecure attachment was associated with his/her spouse’s report of lower relationship quality. Actor–partner mediator models revealed that interpersonal trust mediated the relationship between attachment orientation and relationship quality; insecure attachment was associated with lower levels of interpersonal trust and, in turn, lower relationship quality, both individually and dyadically. Similarly, relationship quality mediated the relationship between attachment orientation and loneliness; insecure attachment was associated with lower relationship quality and, in turn, higher levels of loneliness both individually and dyadically.