The authors present and test the action model of relationship security, which predicts that people's behavior toward a relationship partner shapes their security regarding that partner's care, regard, and commitment. Specifically, actors who enact prosocial or antisocial behavior develop corresponding prosocial or antisocial metaperceptions (i.e., they believe they are viewed as prosocial or antisocial by their partner). In turn, these metaperceptions have a strong influence on actors' security in their partner's care, regard, and commitment due to lay theories positing that prosocial and antisocial behavior impacts others' sentiments. Four studies supported this model. Moreover, findings suggest that prosocial metaperceptions buffer the harmful effects of attachment anxiety on relationship security. This research suggests the relevance of own behavior for relationship security.