What is unjust enrichment?

Unjust enrichment is a legal claim, available even without an enforceable contract, alleging that a defendant unfairly retained a benefit — typically money — at the plaintiff's expense under circumstances that make it unjust for the defendant to keep it. It is frequently pled alongside other claims in consumer class actions as a fallback theory if a specific statutory or contract claim fails.

Unjust enrichment law varies significantly by state, and some states treat it as an independent cause of action while others treat it only as a remedy available once another claim is proven, which affects how nationwide class actions plead this theory across different states. Courts have also split on whether unjust enrichment claims are suitable for class treatment at all, since determining what benefit each class member conferred and whether retaining it was unjust can sometimes require individualized proof that undermines predominance.

Last reviewed 2026-08-22.