This book offers a contractual framework for the regulation of party autonomy in choice of law. The party autonomy rule is the cornerstone of any modern system of choice of law; embodying as it does the freedom enjoyed by parties to a cross-border legal relationship to agree on the law applicable to it. However, as this study shows, the rule has a major shortcoming because it fails to give due regard to the contractual function of the choice of law agreement. The study examines the existing law on choice of law agreements, by reference to the law of both common and civil law jurisdictions and international instruments. Moreover, it suggests a new coherent approach to party autonomy that integrates both the law of contract and choice of law. This important new study should be read with interest by private international law scholars.