The doctrine of unjust enrichment applies the principles of restitution to disputes that are not governed by a contract between the parties. It characterizes the result of a failure to make restitution under circumstances that give rise to an implied or quasi-contractual obligation to return those benefits.

The courts describe this claim in general principles. For example, courts have stated that a claim for unjust enrichment seeks to restore money where equity and good conscience require restitution; it is not premised on wrongdoing, but seeks to determine to which party, in equity, justice, and law, the money belongs; and it seeks to prevent unconscionable loss to the payor and unjust enrichment to the payee.

Because recovery based on unjust enrichment of another party relies on the court's sense of fairness or equity rather than the law, it is often referred to as the equitable doctrine of unjust enrichment.

In Oregon, the doctrine of unjust enrichment is recognized and applied by the courts when one party has received a benefit unjustly at the expense of another, and there is no contractual agreement governing the transaction between them. This doctrine is rooted in principles of equity, aiming to prevent one party from being unjustly enriched at the expense of another. To establish a claim for unjust enrichment in Oregon, a plaintiff must typically demonstrate that (1) they conferred a benefit upon the defendant, (2) the defendant appreciated or knew of the benefit, and (3) it would be inequitable for the defendant to retain the benefit without paying for it. The remedy for unjust enrichment is typically restitution, which is the return of the benefit or its value to the plaintiff. This remedy is not based on the existence of wrongdoing but is instead focused on rectifying situations where it would be unjust for one party to retain a benefit without compensating the other. The courts use their discretion to determine whether, in the interest of fairness and good conscience, restitution is warranted.