I The different scope of party autonomy in the designation of the rules governing the merits in domestic and international court litigation and in arbitration -- A. Party autonomy before domestic courts -- B. Party autonomy in international arbitration: arbitration-specific "conflict rules" -- II The undisputed limitations to the parties’ freedom to determine the applicable substantive rules: overriding mandatory rules and public policy -- III The scope of party autonomy in the selection of the applicable rules -- A. The matters in relation to which the parties are free to designate the applicable rules -- B. The types of rules that can be chosen to govern the merits and the role of non-national rules -- C.The designation of national versus non-national rules -- D. The application of non-national rules in the absence of an explicit designation by the parties? -- IV The implications of the designation of a domestic law -- V The relation between “the law” and party autonomy in the selection of the applicable rules -- A. The crucial role of party autonomy in the designation of the rules governing the merits -- B. The hierarchy between the law and party autonomy -- C. The duties and responsibilities of arbitrators -- Conclusion