The doctrine of subrogation, where one party is substituted to the rights of another, is a remedy familiar to all commercial law practitioners. This book seeks to rationalize the position of the doctrine of subrogation within the general law of restitution. Within a systematic analytical framework, it gives a full account of the developing English and Commonwealth law of subrogation, and a selective use is also made of United States decisions. A number of false assumptions which have entered the case-law are exposed, and the principles upon which subrogation should be awarded are set on a regular basis. Subrogation is a remedy which can be awarded in many different contexts, and this definitive account will be useful not only to restitution lawyers, but also to academics and practitioners concerned with the law of property, commercial law, and even family law.