The article unveils the intellectual indebtedness of Hans J. Morgenthau's realist theory of international power politics to Freudian meta- and group psychology. It examines an unpublished Morgenthau essay about Freudian anthropology written in 1930, placing this work within the context of Morgenthau's magna opera, the 1946 Scientific Man vs. Power Politics and the 1948 Politics among Nations. The article concludes that Morgenthau's international theory is ultimately based on the early instinct theory of Sigmund Freud. Freud is thus to be seen (...) as one of Morgenthau's intellectual fathers. A second main argument refers to the theoretical tradition that Morgenthau has founded within International Relations (IR), namely: political realism. By investigating its core principles, it is argued that realism also may be rooted in Freudian thought. Throughout, the article calls upon IR, Morgenthau scholarship, and international-political theory to take Freud seriously. (shrink)