The law governing the arbitration agreement (law of the AA) determines how the arbitration agreement is interpreted and what jurisdiction a tribunal has. Where parties have not expressly chosen the law of the AA, a number of different approaches exist to determine it. The multiplicity of these approaches juxtaposes uncomfortably against the advantages of arbitration as a predictable and efficient means of alternative dispute resolution. This article conducts a comparative analysis between the approaches used to determine the other laws of international commercial arbitration, namely the curial law and the substantive law, where parties have not chosen them. This article applies common principles drawn from those approaches to set out a preferred approach to determine the law of the AA. It concludes by arguing that a presumption favouring the curial law should arise to apply to the arbitration agreement in the event of a stalemate between the curial and substantive laws.