The goal of the present research was to examine the coregulation of partner-specific attachment security in romantic relationships. We studied a sample of 172 couples 5 times over 1 year. At each assessment wave, partners independently completed a self-report measure of their security in the relationship. We operationalized attachment coregulation both as direct impacts (i.e., prospective effects of one partner on the other) and coordination (i.e., correlated changes across time). Results indicated that, after taking into account people’s prototypical levels of security, changes in security were coordinated within couples.