The psychological relationship between individual and organization has been conceptualized both in terms of identification and in terms of (affective) commitment. In the present study, we explore the differences between these two conceptualizations. Building on the proposition that identification is different from commitment in that identification reflects the self-definitional aspect of organizational membership whereas commitment does not, we propose that commitment is more contingent on social exchange processes that presume that individual and organization are separate entities psychologically, and more closely aligned with (other) job attitudes. In support of these propositions, results of a cross-sectional survey of university faculty (n=133) showed that identification is uniquely aligned (i.e., controlling for affective commitment) with the self-referential aspect of organizational membership, whereas commitment is uniquely related (i.e., controlling for identification) to perceived organizational support, job satisfaction, and turnover intentions. We conclude that the core difference between identification and commitment lies in the implied relationship between individual and organization: Identification reflects psychological oneness, commitment reflects a relationship between separate psychological entities. Copyright © 2006 John Wiley & Sons, Ltd.