Generally speaking, the losing party is more interested than the winning party in understanding the reasons for the outcome of the proceeding. And yet, the requirement that, unless otherwise agreed by the parties, the award "shall state the reasons upon which it is based" is a widely recognized principle in international arbitration. The rules of most arbitral institutions also require that an award include reasons. This Institute Dossier addresses reasoning in International Commercial and Investment Arbitration Awards: Should an arbitrator state his reasons? Why? How extensive and/or complete must the reasoning be for the process to be fully comprehensible and thus legitimate to the parties? What may be the consequences of an unsatisfactory reasoning? Readers will get useful insights into the legal reasoning process by accessing data from a recent large-scale empirical study of legal reasoning in commercial disputes. They will also be treated to some creative writing tips in the hope that reading an award becomes a more interesting part of the job. The ICC Institute of World Business Law brings together the finest legal minds to strengthen links between international business practitioners and the legal profession. The Institute 'Dossiers' is a series that has gained international prestige. These Dossiers are the outcome of the Institute's annual meetings, where experts from around the globe come together to discuss salient issues of international commercial law and arbitration. An ICC Services publication, distributed by Kluwer Law International.