This article examines Otto Rank's psychology and its profound implications for social work knowledge-building and practice. The paper begins with a brief biographical portrait, highlighting the significance of Rank's relationship and eventual break with Freud, and contextualizing the ideas that became the basis for the Functional Approach. We discuss Rank's conception of human functioning in the social environment, his influence on later theories, and a contemporary critique of Rank's ideas. The paper concludes with a discussion of Rank's contributions to the Functional Approach and to social work practice in general.