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 Washington State, the doctrine of unjust enrichment is recognized and applied by 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 and aims to prevent one party from being unjustly enriched at the expense of another. To establish a claim for unjust enrichment in Washington, a plaintiff must demonstrate that (1) the defendant received a benefit, (2) the receipt of the benefit would be unjust without payment for the value of the benefit, and (3) there is no legal justification for the defendant to retain the benefit without paying for it. This remedy is not based on the existence of any wrongdoing but is instead focused on the fairness of the situation and the prevention of an outcome where one party is unjustly disadvantaged while the other is unjustly benefitted. The courts will look at the circumstances of each case to determine if an implied or quasi-contractual obligation exists, and if so, they may order restitution to correct the imbalance.