Contract law (2022): Quasi-contractual obligations: Promissory estoppel (Part One)

Estoppel is a judicial device in common law legal systems whereby a court may prevent or "estop" a person from making assertions or from going back on his or her word; the person being sanctioned is "estopped". Estoppel may prevent someone from bringing a particular claim. Legal doctrines of estoppel are based in both common law and equity. It is also a concept in international law.

Types of estoppel.

There are many different types of estoppel which can arise, but the common thread between them is that a person is restrained from asserting a particular position in law where it would be inequitable to do so. By way of illustration:

If a landlord promises the tenant that he will not exercise his right to terminate a lease, and relying upon that promise the tenant spends money improving the premises, the doctrine of promissory estoppel may prevent the landlord from exercising a right to terminate, even though his promise might not otherwise have been legally binding as a contract. The landlord is precluded from asserting a specific right.

If a person brings legal proceedings in one country claiming that a second person negligently injured them and the courts of that country determine that there was no negligence, then under the doctrine of issue estoppel the first person will not normally be able to argue before the courts of another country that the second person was negligent (whether in respect of the same claim or a related claim). The first person is precluded from asserting a specific claim.

Estoppel is an equitable doctrine. Accordingly, any person wishing to assert an estoppel must normally come to the court with "clean hands".

The doctrine of estoppel (which may prevent a party from asserting a right) is often confused with the doctrine of waiver (which relates to relinquishing a right once it has arisen). It also substantially overlaps with, but is distinct from, the equitable doctrine of laches.