This chapter presents the lawsuit of the Belgian deportees examined by the German-Belgian MAT in 1923-24, a single case with major political ramifications. Between 1916 and 1918, Germany had deported tens of thousands of Belgian workers as forced labourers for its war-relevant industries and armed forces, sparking an international outcry amongst both Allied and neutral states. Pursuant to Part VIII of the Versailles Treaty, Germany was under the obligation to compensate Belgium for these deportations to forced labour. However, when the former deportees realised that the sums agreed to by Germany and partly handed out to them by the Belgian State were far below their expectations, they tried to obtain satisfaction before the Belgian-German MAT. Coordinated by a young Brussels lawyer, Jacques Pirenne, this early example of international legal mobilisation was followed with concern by both Germany and Belgium. Both feared that were the Belgian-German MAT to accept jurisdiction over the deportees’ claims, this might considerably increase Germany’s war debt vis-à-vis Belgium, thus further deteriorating the relations between both countries which were already strained because of the Ruhr crisis. Relying in part on previously uncommented archival material from Belgium, Germany and France and using contemporary press reports, including photographs, the chapter provides the reader with an in-depth description and analysis of the trial during its various procedural stages. After presenting the reader with the factual and legal background of the case, it takes a close look at the arguments of the parties during both the written and the oral phases of the proceedings. Analysing the MAT’s decision, it questions its frequent characterisation as a major German victory, before concluding on its long-term legacy.