A quasi-contract, also an implied-in-law contract, is a legal substitute for a contract. A quasi-contract is a contract that should have been formed, even though in actuality it was not. It is used when a court wishes to create an obligation upon a non-contracting party to avoid injustice.

An example of a quasi-contract is the case of a plumber who accidentally installs a sprinkler system in the lawn of the wrong house. The owner of the house had learned the previous day that his neighbor was getting new sprinklers. That morning, he sees the plumber installing them in his own lawn. Pleased at the mistake, he says nothing, and then refuses to pay when the plumber hands him the bill. Will the man be held liable for payment? Yes, if it could be proven that the man knew that the sprinklers were being installed mistakenly, the court would make him pay because of a quasi-contract. If that knowledge could not be proven, he would not be liable.

See also

• Contract
• promissory estoppel