On the basis of an interdependence analysis, it is proposed that commitment to a close relationship is associated with cognitive interdependence—a mental state characterized by a pluralistic, collective representation of the self-in-relationship. A cross-sectional survey study and a 2-wave longitudinal study revealed that strong commitment to a romantic relationship is associated with greater spontaneous plural pronoun usage, greater perceived unity of self and partner, and greater reported relationship centrality. Commitment and cognitive interdependence operate in a cycle of mutual influence, such that earlier commitment predicts change over time in cognitive interdependence, and earlier cognitive interdependence predicts change over time in commitment. Links between commitment and cognitive interdependence were weak or nonsignificant for relationships among best friends, suggesting that this phenomenon may be unique to romantic relationships.