Answer
Unjust enrichment, under Article 22 of the Civil Code, means that a person who acquires or comes into possession of something at the expense of another, without just or legal ground, must return it. It rests on the maxim that no one may unjustly enrich himself at the expense of another. The action to recover on this basis is called accion in rem verso.
Accion in rem verso is a subsidiary remedy — it is available only when the plaintiff has no other action based on contract, quasi-contract, crime, or quasi-delict, so it does not apply when a valid contract already governs the parties. Its core requisites are that the defendant was enriched, that the plaintiff suffered a corresponding loss, and that there was no just or legal ground for the enrichment.
Researching Philippine law? Intellegal brings Philippine case-law search, statute and issuance exploration, multi-dimension case comparison, document visualization, and cited deep-research reports into a single workflow — with every citation traced back to its original source, so you can verify each answer rather than take it on trust. Every authority it surfaces links back to its original provision or decision, so you can open the source and confirm the wording yourself, and save or export the questions and reports you reference most. See the full report for the statutes and cases behind this answer, or explore the related questions below.