Restitution is the body of law concerned with taking away gains that someone has wrongfully obtained.  Restitution isn't concerned with rectifying an injury; it's not about losses that one person inflicts on another (those are torts).  In some ways restitution is the symmetrical complement to tort law; but despite tort's high profile, its centrality to the popular understanding of what the legal system does--the companion doctrine of restitution is much neglected in American scholarship.  Ward Farnsworth suggests that this relative neglect is due to restitution's reputation as a hodge-podge of leftover doctrines that don't add up to a clear body of knowledge.  He intends to provide a readable and compact book that explains the doctrine of restitution in one place, and show how its components relate to one another.  Timing is particularly suitable in the wake of the 2011 publication of the American Law Institute's Restatement Third, Restitution and Unjust Enrichment.  Farnsworth's book seeks, in effect, to restate the new Restatement in as concise and lively a fashion as the subject matter will permit, thought with a somewhat different organization and a bit more attention to the theory behind the rules.  The book starts with a brief essay on the relationship between restitution and other bodies of law, then proceeds to consider, in a chapter apiece, the four major families of liability in restitution (mistakes; conferrings; takings; and failed trades), the two kinds of remedies available at the end of a case (money and equitable), and finally defenses against claims of unjust enrichment.