The purpose of this article is to try and synthesize the views that have been put forward to date and analyze them in a comprehensive framework. The article begins with an analysis of:(1) the concept of mandatory rules;(2) the position of the debate within international commercial arbitration;(3) the sometimes overlooked distinction between issues of jurisdiction and the application of mandatory rules;(4) legal and policy arguments for the application of mandatory rules; and(5) the relevance of party autonomy and possible types of evidence of consent for or against the application of mandatory rules.This leads on to a critical analysis of the suggestions postulated by leading authors, organisations and treaties, and finally, an evaluation of the various individual factors that may come into play if an arbitrator is found to have a discretion as to whether to apply mandatory rules in the absence of express consent from the parties.