Raymond Aron is often considered one of the greatest modern theorists of realism. However, one may question this way of classifying Aron. Indeed an attentive reading of his work reveals a singular approach that is based on two criticisms. The first one reproaches the classical liberal tradition for having engendered illusory projects. The second one is directed to a cold war realism that is accused of transforming itself into a simplistic ideology. Thus the originality of Aron’s approach resides in its attempt to overcome the classical opposition between the two schools, while preserving what is most valuable in them. That’s why one proposed to consider Aron as a heterodox realist, namely as an advocate of a « post-Kantian machiavellianism ».