Unjust enrichment is a legal term denoting a particular type of causative event in which one party is unjustly enriched at the expense of another, and an obligation to make restitution arises, regardless of liability for wrongdoing.

Definition:
1. n. A benefit by mistake or chance. Morally and ethically the one who gains a benefit that he or she has not paid or worked for should not keep it to the rightful owner's detriment. The party that received money, services or property that should have been delivered to or belonged to another must make restitution to the rightful owner. A court may order such restitution in a lawsuit brought by the party who should rightly have the money or property.

2. n. A general equitable principle that a person should not profit at another's expense and therefore should make restitution for the reasonable value of any property, services, or other benefits that have been unfairly received and retained.

A common example is when a party contracts to provide a service, but the contract is terminated prematurely due to a breach, and the contractor unjustly receives no compensation for partial services rendered.