Chapter 5 addresses the German–Polish Convention of 15 May 1922, a legal instrument that was negotiated with the direct participation of the League Secretariat and whose aim was the smooth partition of the multi-ethnic industrial region of Upper Silesia. It shows that while this treaty provided opportunities for ‘peace through law’, it ultimately failed to meet this expectation. After providing an overview of the Convention’s drafting process and its key features, notably its reliance on international procedural avenues to guarantee individual rights, the chapter examines these guarantees and how they came into being. It then focusses on the role of the president of the Mixed Commission for Upper Silesia, Felix Calonder, a vocal proponent of ‘peace through law’. In his role as local guarantor of minority rights, Calonder developed a systematic case law that was unequalled before the advent of the international human rights law bodies after the Second World War and foreshadowed some of the principles adopted by them. It concludes by reflecting on the various limitations that this law shared with other attempts to use legal techniques to solve interstate conflicts of the interwar period.