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 Arizona, 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 valid contract governing the transaction between the parties. This doctrine is rooted in principles of equity, aiming to prevent one party from being unjustly enriched at the expense of another. Arizona courts will consider an unjust enrichment claim when a party has received a benefit that in fairness and good conscience should be paid for. The claim is not based on the existence of wrongdoing but on the equitable principle that it is unjust for a person to retain a benefit without paying for it when it would be inequitable to do so. 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 the party who provided the benefit. This remedy is designed to prevent one party from suffering an unconscionable loss while the other is unjustly enriched.