This article approaches the International Court of Justice (ICJ) and its decisions from the lens of “deformalization”. It conceptualises “deformalization” not in a de-institutionalised sense, but as implying informality within the functioning of formal institutions. It posits that it may be useful to adopt this perspective to examine some of the actions of the ICJ, which may not be adequately explained from a purely formal standpoint. It examines various areas of deformalization within the ICJ, such as its approach towards evidence or provisional measures. It attempts to understand why and when deformalization is needed by the ICJ and concludes that the ICJ walks a tightrope between formal rules and informal application, in order to improve its effectiveness and legitimacy.