What is "estoppel"

Estoppel \Es*top"pel\, n. [From Estop.] (Law)

1. A stop; an obstruction or bar to one's alleging or denying a fact contrary to his own previous action, allegation, or denial; an admission, by words or conduct, which induces another to purchase rights, against which the party making such admission can not take a position inconsistent with the admission.

2. The agency by which the law excludes evidence to dispute certain admissions, which the policy of the law treats as indisputable.
   --Wharton.
   --Stephen.
   --Burrill.

1530s, from estop, or from Old French estopail "bung, cork," from estoper.

n. (context common law English) A legal principle in the law of equity that prevents a party from asserting otherwise valid legal rights against another party because conduct by the first party, or circumstances to which the first party has knowingly contributed, make it unjust for those rights to be asserted.

n. a rule of evidence whereby a person is barred from denying the truth of a fact that has already been settled

Estoppel is a collective name given to a group of legal doctrines in common law legal systems whereby a person is prevented from making assertions that are contradictory to their prior postion on certain matters before the court - the person is said to be "estopped". Estoppel may operate by way of preventing someone from asserting a particular fact in court, or exercising a certain right, or from bringing a particular claim. Black's Law Dictionary defines estoppel as a "bar or impediment raised by the law, which precludes a man from alleging or from denying a certain fact or state of facts, in consequence of his previous allegation or denial or conduct or admission, or in consequence of a final adjudication of the matter in a court of law."

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.

The word is derived from the 16th century French word "estouppail."

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.