This volume explores the relationship between form and substance in the law of obligations. It builds on the rich tradition of legal thought that deploys the concepts of form and substance to inform our understanding of the common law. The essays in this collection offer multiple conceptions of form and substance and cover an array of private law subjects, scholarly approaches and jurisdictions. The collection makes it clear that the interplay between form and substance is a key element of the dynamism that characterises this area of the law.