Unjust enrichment in the civil law of property and obligations: requirements, subsidiarity and limitation of the action

The unjust enrichment action has become established as a cross-cutting instrument of the civil law of property and obligations, used to correct situations in which one person is enriched at the expense of another without any legal cause justifying it and without any specific action for restitution being available. Its make-up requires enrichment, correlative impoverishment, absence of cause and subsidiarity in relation to other avenues, together with its careful distinction from undue payment, civil liability and contractual actions. STS 271/2026 of 20 February makes a highly topical contribution by examining an unjust enrichment action and addressing when prior criminal proceedings may interrupt the limitation period for the subsequent civil action, requiring a substantial connection between the facts investigated in the criminal proceedings and those underpinning the civil claim.

24/03/2026

Property and contract law Litigation

1.The concept of unjust enrichment and its requirements

Unjust enrichment takes the form of an action of a quasi-contractual nature which allows restitution of what has been improperly received to be claimed where there is no legal title legitimising the transfer of value and no other specific action is available. Academic commentary and case law have identified four basic requirements. First, there must be enrichment of one person, understood as an increase in that person's assets or the avoidance of a loss which he or she should reasonably have borne. Second, there must be a correlative impoverishment of another, taking the form of a reduction in assets or the assumption of a burden which was not his or hers to bear. Third, there must be no legal cause justifying the transfer of value, that is to say, there must be no valid contract, statutory provision, effective unilateral act or any other title legitimising the enrichment. Fourth, the action must be subsidiary, so that it is available only where the legal system offers no other specific action to correct the situation, such as the contractual action, the civil liability action or the action for recovery of an undue payment, the Spanish “pago de lo indebido”.

Subsidiarity is an essential feature. Unjust enrichment cannot be used to circumvent the requirements, time limits or restrictions of specific actions. Where there is a contract governing the relationship, the natural avenue will be the contractual action; where there is an unlawful act, the action in non-contractual liability; where a payment has been made without any legal obligation to do so, the undue payment action. Only where those avenues are unavailable or have been closed off for reasons unconnected with the claimant's conduct can the unjust enrichment action perform its corrective function.

2.Distinguishing unjust enrichment from undue payment, civil liability and contractual actions

Distinguishing unjust enrichment from neighbouring figures is crucial in order to avoid overlaps and distortions. Undue payment, which is governed by the “Código Civil” —Spain's Civil Code—, covers the situation in which something is handed over which there was no right to receive and which has been improperly delivered by mistake, giving rise to the obligation to return it. A mistake in the payment is presumed where something was delivered which was never owed or which had already been paid, although the recipient may prove that the delivery was made by way of gift or on some other just cause. The undue payment action focuses on the existence of a payment made without any obligation and on the mistake of the solvens, and it provides a specific avenue for restitution. Where its requirements are met, it displaces the unjust enrichment action, which is reserved for situations in which there is no undue payment as such, but rather other transfers of value without cause.

Non-contractual civil liability, for its part, is built around the causing of unlawful damage by a negligent or wilful act or omission, and requires fault, damage and a causal link. The unjust enrichment action requires neither fault nor damage in the strict sense, but rather an unjustified imbalance between the parties' assets. In many cases the same situation may be analysed from both perspectives, but the choice of avenue has consequences in terms of evidential requirements, limitation periods and the extent of the compensation. The subsidiarity of unjust enrichment means that, if the damage can be brought within civil liability, that will be the preferred avenue.

Contractual actions, finally, are founded on the breach of obligations assumed under a valid contract. Where a contract exists, the general rule is that disputes are to be resolved within its framework, by way of claims for performance, termination or damages. Unjust enrichment cannot serve to reshape a contract or to correct imbalances arising from its content, unless the contract is void or ineffective and no other specific action is available to restore what has been performed. The case law has been particularly careful to prevent the unjust enrichment action from becoming an instrument for getting round the limitation of contractual actions or for reopening closed litigation.

3.Limitation of the unjust enrichment action and article 1964 CC

The unjust enrichment action, as a personal action for which no special period is laid down, is subject to the general limitation regime in article 1964 of the Civil Code, which provides that personal actions for which no special period is laid down are barred by limitation five years after performance of the obligation may be demanded, and that in the case of continuing obligations to do or not to do, the period will begin to run each time they are breached. Determining the dies a quo requires identifying the point at which the claimant could reasonably have become aware of the enrichment, the impoverishment and the absence of cause, and at which the action was in a position to be brought.

Limitation sits within the general framework of article 1930 CC, which provides that ownership and other rights in rem are acquired by prescription in the manner and on the conditions laid down by law, and that rights and actions of whatever kind are likewise extinguished by limitation. The interpretation of limitation is traditionally restrictive, in the sense that doubts as to when the period begins to run should not be resolved to the detriment of the holder of the action, particularly where the complexity of the facts makes it difficult to identify the point at which the action could have been brought.

4.Prior criminal proceedings and interruption of the limitation period: STS 271/2026

STS 271/2026 of 20 February makes a significant contribution by examining an unjust enrichment action and addressing when prior criminal proceedings may interrupt the limitation period for the subsequent civil action. In that case, the claimant had suffered an unjustified transfer of value arising from the conduct of a company which improperly contributed a plot of land belonging to him to a “Junta de Compensación”, the landowners' board set up to carry out an urban development scheme. Following a final judgment recognising his ownership and ordering the company and the board to return the plot or its value, enforcement proved fruitless because both entities had been dissolved. The claimant subsequently brought liability actions against the directors, which were dismissed on limitation grounds, and lodged a criminal complaint —a “querella”— for fraud against the director, which ended in an acquittal. He finally brought an unjust enrichment action against the shareholders of the dissolved company.

Both the court of first instance and the “Audiencia Provincial”, the provincial appeal court, held that the unjust enrichment action was barred by limitation, applying the fifteen-year period then in force for personal actions and running it from the moment the claimant became aware of the company's dissolution. The “Tribunal Supremo”, Spain's Supreme Court, allows the cassation appeal and sets that finding aside, taking the view that the conduct of the criminal proceedings interrupted the limitation period for the civil action, in application of the doctrine on criminal preliminary questions —“prejudicialidad penal”— and of actio nondum nata non praescribitur.

The Chamber recalls that the pendency of criminal proceedings concerning the same facts constitutes a legal obstacle to bringing the civil action, and postpones the start of the limitation period. The key lies in the objective connection between the facts investigated in the criminal proceedings and those on which the civil claim is based. Identity of parties is not required, but rather substantial identity of facts and the possibility that the criminal decision may have a decisive influence on the outcome of the civil matter. In that case, the facts tried in the criminal proceedings against the director, concerning the misappropriation of the plot and the concealment of the company's dissolution in order to frustrate enforcement of the civil judgment, were substantially the same as those underpinning the unjust enrichment action against the shareholders. The criminal decision, whether a conviction or an acquittal, was capable of having a material bearing on the assessment of the enrichment and of the absence of cause.

On that basis, the Supreme Court concludes that the commencement of the criminal proceedings interrupted the limitation period for the civil action and that it did not start to run again until the criminal judgment became final. Since the unjust enrichment claim was lodged within the fresh period, the action was not barred by limitation. The judgment stresses that interruption of limitation by criminal proceedings does not require identity of parties between the two sets of proceedings, but rather a substantial connection of facts, and that limitation cannot be used to close off the civil avenue while the injured party is legitimately awaiting the criminal decision.

5.Subsidiarity, the criminal connection and litigation strategy

STS 271/2026 highlights the importance of the subsidiarity of unjust enrichment and of the coordination between the criminal and civil avenues. The unjust enrichment action is brought in a context in which other avenues, such as enforcement of the initial civil judgment and liability actions against directors, have proved fruitless or have been closed off by limitation. The choice of the criminal avenue, by way of a criminal complaint for fraud, reflects the seriousness of the facts and the need to clarify the director's conduct. The subsequent unjust enrichment action against the shareholders is presented as a subsidiary remedy for correcting the unjustified transfer of value.

The substantial connection between the criminal and civil facts allows the pendency of the criminal proceedings to interrupt the limitation period for the civil action, but it also calls for a carefully considered litigation strategy. The injured party must assess whether the criminal avenue is necessary and proportionate, and must be aware that the civil action may be held in abeyance while the criminal proceedings run their course. The doctrine laid down in STS 271/2026 provides certainty by confirming that limitation will not run during that period, provided that the connection of facts is clear and that the criminal decision is capable of influencing the civil outcome.

For litigation practice, the judgment is particularly useful because it clarifies that the interruption of limitation by criminal proceedings is not confined to typical civil liability actions, but extends to unjust enrichment actions where the facts substantially coincide. It also reinforces the idea that limitation must be interpreted restrictively and that doubts as to the dies a quo should not be resolved to the detriment of the injured party.

6.Conclusion: unjust enrichment, subsidiarity and limitation after STS 271/2026

Unjust enrichment is confirmed as a cross-cutting institution of the civil law of property and obligations, designed to correct situations in which someone is enriched at another's expense without legal cause and without any other specific action for restitution being available. Bringing the action requires proof of enrichment, correlative impoverishment, absence of cause and subsidiarity in relation to other avenues, and requires it to be carefully distinguished from undue payment, civil liability and contractual actions. Limitation of the action is governed by article 1964 of the Civil Code, with a restrictive interpretation of the dies a quo and attention to the point at which the claimant could become aware of the imbalance between the parties' assets and the lack of cause.

STS 271/2026 adds a key element by showing how prior criminal proceedings may interrupt the limitation period for the unjust enrichment action, provided that there is a substantial connection between the facts investigated in the criminal proceedings and those underpinning the civil claim. The requirement of objective identity of facts, rather than of parties, and the statement that limitation must not operate against the injured party while he or she is legitimately awaiting the criminal decision, provide valuable guidance for litigation strategy and for framing the unjust enrichment action in complex situations.

Alburquerque AbogadosJosé Manuel AlburquerqueBarcelona 24/03/2026

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