The fourth edition of _The Principles of the Law of Restitution_ brings this widely cited and influential volume fully up to date. Substantially rewritten to reflect significant changes in the law of restitution and the expansion in the theoretical and critical commentary on the subject, this book is grounded in its clarity of exposition and analysis. The new edition significantly expands existing chapters on the treatment of the history of unjust enrichment, enrichment, the treatment of legally effective bases for receipt, and compulsion. It further expands existing parts on restitution for wrongs and proprietary restitutionary claims as well as offering completely new chapters dealing with 'at the claimant's expense', 'absence of intent', and the defence of illegality. Focusing primarily on English law, the volume also engages with the law in other common law jurisdictions, notably Australia, Canada, New Zealand, and Singapore. It provides a clear exposition of complex areas of law as well as critical analysis of that law. Timely and comprehensive, this book provides readers with a crucial guide to the law of restitution and will continue to be invaluable to student, academics, and practitioners alike.