The issue of applicable law is something that all investment tribunals must inevitably address. Yet it is one of the most misunderstood and misaddressed (or ignored) topics in the field. The basics of applicable law are relatively straightforward – the law applicable to the dispute is that which arbitrators use to come to a decision about whether or not there has been a breach of that law. Thus, whether they are adjudicating a contractual or treaty-based dispute, investment arbitrators must first identify the law applicable to the dispute and then use it to assess the liability of the defending party or parties. These statements are deceptively simple, since the selection of applicable law, its application, and its intersection with other laws, whether international or domestic, continue to be contentious and difficult questions.