Unjust enrichment
From Roman law, in both traditions
Contract and obligationsBasic ideas
What it means
The idea that a person who has received a benefit at another's expense, with no legal ground for keeping it, must give it back. It covers money paid by mistake, benefits received under a contract that turns out to be void, and many other cases.
Why it travels badly
Civil-law codes state this as a general principle with its own chapter. English law for a long time had only separate remedies, such as 'money had and received' and 'quasi-contract', and accepted a general principle of unjust enrichment only late in the twentieth century. So the same idea sits under different labels, in different places, with different reach.
How other systems say it
ungerechtfertigte Bereicherung (§ 812 BGB)
A person who obtains something at another's expense without legal ground must give it back. The Code sets out several kinds of claim.
enrichissement sans cause (arts 1303 to 1303-4 Code civil)
A general principle, written into the Code in the 2016 reform after a long history in the case law.
unjust enrichment / restitution
Recognised as its own area of law in Lipkin Gorman v Karpnale (1991). The claimant must show that the defendant was enriched, at the claimant's expense, and that the enrichment was unjust.
United States
restitution and unjust enrichment
Summarised in the Restatement (Third) of Restitution and Unjust Enrichment. The label 'quasi-contract' is still used by some courts.
Tip for translators and students
Do not translate 'restitution' as 'restitución' or 'Rückerstattung' without checking: in some systems the word means giving back property or undoing a contract, not the general claim.
Related: Obligation and Schuldrecht, Good faith, Equity
Updated October 2026. Spotted a mistake? Tell us.
TheLawToKnow Tools’s glossary is an educational overview of the main differences between legal systems. It is not legal advice.
