Hans Morgenthau was a founder of the modern discipline of International Relations, and his Politics among Nations was for decades the dominant textbook in the field. The character of his Realism has frequently been discussed in debates on methodology and the nature of theory in International Relations. Almost all of this discussion has mischaracterized his views. The clues given in his writings, as well as his biography, point directly to Max Weber’s methodological writings. Morgenthau, it is argued, was a sophisticated user of Weber’s views who self-consciously applied them in the sphere of International Relations in such a way that Realism provided an ideal-typical model of the rational and responsible statesman. This interpretation both explains Morgenthau’s views and shows them to be a serious, complex, and compelling response to the issues which have animated the controversies over International Relations theory after Waltz’s presentation of the methodological basis for his neo-Realism.