F. Oppenheimer's System der Soziologie is a multivolume publication that contains a general sociology as a common basis for all social sciences; a theory of development; as well as specialized sociologies: sociology of the economy, of law, of the state, etc. Oppenheimer conceived sociology as a historically grounded universal science. Ibn Khaldun came into play in relationship with Oppenheimer's state theory. His approach directly built on Gumplowicz's “sociological state theory”. An overview on Oppenheimer's works shows that Ibn Khaldun was by no means the starting point of theorization on the state. We do not find any reference to him in an earlier publication, Der Staat (1912), that already contained the full elaboration of Oppenheimer's theory. Nevertheless, his reception of Ibn Khaldun is important: Ibn Khaldun was mobilized within the framework of a scholarly debate that was ongoing amongst European sociologists at the time, and whose key representative, Ludwig Gumplowicz, contributed significantly to his reception in the concerned period. In this context, Oppenheimer did not merely mention Ibn Khaldun in an encyclopaedic endeavor to present a complete overview on “precursors” of sociology, but as a representative and contributor to a theoretical approach which, Oppenheimer believed, they both shared.