This chapter discusses the appropriate types of expertise that should be available in the composition of international courts. The main argument is that the international bench needs to include judges with diverse and specialised expertise. For this reason, the concept ‘competence in international law’ as a statutory requirement for nomination and election of judges can be construed broadly, seeking out individuals who not only have recognised competence in international law sensu stricto but also strong complementary knowledge in specialised area(s) of international law relevant to a given court’s judicial work. Judges who are conversant with both general and special aspects and areas of international law are well placed to navigate the complexity and density of international law entrenched in disputes submitted for international adjudication. The first part of the discussion engages with the idea that general international courts value expertise of judges in specialised areas of international law and that specialised international courts value judges with competence in international law. Existing statutory election requirements can accommodate this suggestion. The second part of the discussion explores the detailed expertise requirements incorporated in the statutes of certain, new international courts. Novel developments suggest a turn towards favouring and quantifying required expertise in different areas of international law when deciding the overall composition of a court.