This Chapter seeks to appraise the Tokyo International Military Tribunal (IMT)’s approach to what was then called crimes against peace (or, in more modern parlance, the crime of aggression). The Tokyo IMT was primarily concerned with the crime of aggression, and as such the Chapter situates the foundational documents of the Tokyo IMT, such as its statute, indictment, and the debates that surrounded them, against that background. The Chapter then looks at the way in which the arguments that continue to bedevil debates about aggression played out in the Majority judgment, and the separate/dissenting opinions that accompanied it. It attempts to do with respect to both the law, the various and contested facts that the various opinions based themselves upon, alongside the application of the law to those different views of the situation leading up to the conflict(s)that were relied upon. Having canvassed these issues, the Chapter concludes by drawing parallels between the issues that arose before the Tokyo IMT and those that are now still being debated with respect to aggression, unfortunately, often without reference to the complex, and controversial matters that arose in Tokyo.