John Anderson, Professor of Philosophy at the University of Sydney from 1927 to 1958, is not conventionally viewed as having exerted a significant influence on the development of international relations in the 20th century. Indeed, his contributions to philosophical realism and public debate in Australian society have been more readily acknowledged as his major spheres of influence. However, Anderson must also be credited with having exerted a significant influence on the intellectual development of one of the most prominent international relations theorists of the 20th century, his student Hedley Bull. With this in mind, this article assesses the impact of Anderson's teachings on Bull's thought and argues that although Bull deviated from his earliest mentor's more extreme views about ethical inquiry, his general approach to the study of international relations, understanding of international society, and sceptical attitude towards religion can, in large part, be derived from Anderson's teachings.