The rendering of the judgment in the case of Prosecutor v. Ratko Mladić on 22 November 2017 was a defining moment in the history of modern international criminal law. The first indictment against Ratko Mladić had been issued almost 20 years prior, during the early years of the ICTY. The judgment marked the end not only of the five year-trial but also of the work of the ICTY. As one of the biggest war crimes trials in history, it presents numerous challenges and lessons that are relevant for other present and future international courts and tribunals. Jonas Nilsson was the Senior Legal Officer advising the Trial Chamber throughout the pre-trial and trial proceedings in this case. He is therefore in a unique position to give an insider’s perspective to these challenges and lessons.