Enrichment is key to understanding the law of unjust enrichment and restitution. This book provides a comprehensive analysis of the concept of enrichment and its implications for restitutionary awards. The book argues that enrichment may be characterized as either factual or legal, and it explores the consequences of that distinction. In factual enrichment cases, the measure of enrichment is the objective value received. This is the basis of awards of money had and received, quantum meruit, quantum valebat, and money paid. In legal enrichment cases, the benefit is the acquisition of a specific right or the release of a specific obligation. The remedy is restitution of that right or reinstatement of that obligation. It is demonstrated that specific restitution of the defendant's legal enrichment is the basis for certain resulting trusts, rescission, rectification, and subrogation. The book has profound implications for understanding restitutionary awards and the relationship between the enrichment inquiry and other aspects of the law of unjust enrichment, including the 'at the expense of' inquiry and the defense of change of position. It will be of interest to all those specializing in restitution and unjust enrichment. (Series: Hart Studies in Private Law - Vol. 3)