There are currently no prosecutions of individuals for having committed the crime of aggression or what is sometimes called the crime against peace. One fairly good reason for this fact is that there is no treaty or international statute that defines this international crime and sets out the elements that a prosecutor would have to prove to convict someone of violating it. There were prosecutions by the International Military Tribunal at Nuremberg, and the subsequent trials at Nuremberg just after World War II, but for various reasons that I will rehearse in this chapter, the Nuremberg prosecutions for crimes against peace have not been seen as establishing a “precedent.” I will examine what the basis of such trials was said to be and why there has been such reluctance to use similar rationales today.