Attachment theory proposes that experiences of acceptance and rejection will modify feelings of attachment security, but such processes have rarely been investigated. In this study, daily variations in attachment anxiety and avoidance were investigated across 7 days in a sample of college undergraduates currently in romantic relationships. We observed significant within-person variation in attachment avoidance and anxiety. Participants reported lower anxiety and avoidance on days on which they felt more accepted by their romantic partners. Further, perceptions of acceptance predicted the following day's attachment security through lower negative mood. Greater variability in attachment avoidance and anxiety was associated with greater physical aggression in relationships. (C) 2016 Elsevier Inc. All rights reserved.