This new book, written by the editor of the Clarendon Law Series, is a tightly structured, clear and concise account of the law of unjust enrichment, and attempts to move away from the usage of obscure terminology inherited from the past. Over the past half-century the law of restitution has made great progress and is now widely accepted as being an indispensible core subject of the common law. However, there is still further progress to be made and this text is the first book in England to switch from restitution to unjust enrichment, and from response to event. It organises modern law around five simple questions: Was the defendent enriched? If so, was it at the claimant's expense? If so, was it unjust? The claimant must then ask what kind of rights he has and the defences he may face. This book provides a concise and stimulating introduction to the subject that will be ideal for students and specialists.