The role played by the International Court of Justice (and, formerly, its predecessor, the Permanent Court of International Justice) in the development of international law has been debated by scholars almost since the establishment of the World Court in 1922. While most agree that the ICJ has an influence in this regard, there is little agreement beyond that. This article, which draws upon a 2013 edited collection of the same name involving studies by leading experts in over a dozen areas of international law, posits some parameters appertaining to the influence of the Court. In short, it is suggested that the answer to the question whether the Court contributes to the development of international law in a meaningful way depends, in large measure, on the particular area of international law. This is so because important factors – including how frequently the ICJ is called upon to consider the area, what other law-determining agents exist in the area and the nature of the applicable international law – vary depending on the subject area. The article tests the proposed parameters through a brief consideration of the ICJ’s influence on the international law regarding the functioning of the United Nations.