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 Maine, 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 them. This doctrine is rooted in principles of equity, aiming to prevent one party from being unjustly enriched at the expense of another. Maine courts will consider factors such as whether the enrichment was at the expense of the claimant, whether the enrichment was unjust, and whether there is a legal justification for the retention of the benefit. If the court finds that these elements are met, it may impose a quasi-contractual obligation to return the benefit or its value, even though no actual contract exists. This is to ensure that equity and good conscience govern the outcome, and to prevent one party from retaining a benefit that rightfully belongs to another. It is important to note that claims of unjust enrichment are highly fact-specific and the outcome can vary depending on the circumstances of each case. An attorney can provide guidance on how the doctrine might apply to a particular situation in Maine.