Estoppel is a doctrine in common law jurisdictions recognized both at law and in equity in various forms. In general it protects a party who would suffer detriment if the defendant has done or said something to induce an expectation. The plaintiff relied (reasonably) on the expectation, and would suffer detriment if that expectation were false.

Unconscionability by the defendant has been recognized as another element by courts, in an attempt to unify the many individual rules of estoppel. In most cases, it is only a defense that prevents a plaintiff from enforcing legal rights, or from relying on a set of facts that would give rise to enforceable rights (e.g. words said or actions performed) if that enforcement or reliance would be unfair to the defendant. Because its effect is to defeat generally enforceable legal rights, the scope of the remedy is often limited.

For an example of estoppel, think about the case of a debtor and a creditor. The creditor might unofficially inform the debtor that the debt has been forgiven. Even if the original contract was not terminated, the creditor may be stopped from collecting the debt if he changes his mind later. It would be unfair to allow the creditor to change his mind in light of the unofficial agreement he made with the debtor beforehand. In the same way, a landlord might inform a tenant that rent has been reduced, for example, if there is construction or a lapse in utility services. If the tenant relies on this advice, the landlord could be stopped from collecting rent retroactively.

Estoppel is closely related to the doctrines of waiver, variation, and election and is applied in many areas of law, including insurance, banking, employment, international trade, etc. In English law, the concept of legitimate expectation in the realm of administrative law and judicial review is estoppels counterpart in public law, albeit subtle but important differences exist.

This term appears to come from the French estoupail or a variation, which meant "stopper plug", referring to placing a halt on the imbalance of the situation. Ultimately, it comes from the Latin stopare, "to stop".



Estoppel in English law is defined as: "a principle of justice and of equity. It comes to this: when a man, by his words or conduct, has led another to believe in a particular state of affairs, he will not be allowed to go back on it when it would be unjust or inequitable for him to do so."

The definition in American law is similar: "Speaking generally, Estoppel is a bar which precludes a person from denying or asserting anything to the contrary of that which has, in contemplation of law, been established as the truth, either by the acts of judicial or legislative officers, or by his own deed, acts, or representations, either express or implied."

Major Types:

The main species of estoppel under English, Australian, and American laws are:

  • Estoppel by Record: This frequently arises as issue/cause of action estoppel, judicial estoppel or res judicata where the orders or judgments made in previous legal proceedings prevent the parties from re-litigating the same issues or causes of action,
  • Estoppel by Deed: Where rules of evidence (often regarded as technical or formal estoppels) prevent a litigant from denying the truth of what was said or done, and
  • Reliance-based Estoppels: These are the most important forms. This class includes estoppel by representation of fact, promissory estoppel and proprietary estoppel.
  • Estoppel by representation of fact is known as equitable estoppel in American law.
  • Equitable Estoppel as understood in English law, includes:
  • Promissory Estoppel
  • Proprietary Estoppel

Although some authorities regard reliance-based estoppels as mere rules of evidence, they are in reality rules of substantive law. Laches is estoppel by delay. Laches has been considered both a reliance-based estoppel, and a sui generis type of estoppel.

Reliance-based Estoppels:

Under English law, estoppel may be by representation of fact, where one person asserts the truth of a set of facts to another, promissory estoppel, where one person makes a promise to another, but there is no enforceable contract, and proprietary estoppel, where the parties are litigating the title to land.

These are regarded as reliance-based estoppels. Regarded as estoppels by representation. More simply, one party must say or do something and see the other party rely on what is said or done to change behavior.

To establish a reliance-based estoppel, the victimized party must be able to show both inducement and detrimental reliance, i.e., there must be evidence to show that the representor actually intended the victim to act on the representation or promise, or the victim must satisfy the court that it was reasonable for him or her to act on the relevant representation or promise, and what the victim did must either have been reasonable, or the victim did what the representor intended, and the victim would suffer a loss or detriment if the representor was allowed to deny what was said or done, detriment is measured at the time when the representor proposes to deny the representation or withdraw the promise, not at the time when either was made, and in all the circumstances, the behavior of the representor is such that it would be "unconscionable" to allow him or her to renege.

Estoppel by representation of fact and promissory estoppel are mutually exclusive, the former is based on a representation of existing fact (or of mixed fact and law), while the latter is based on a promise not to enforce some pre-existing right (i.e. it expresses an intention as to the future). A proprietary estoppel operates only between parties who, at the time of the representation, were in an existing relationship, while this is not a requirement for estoppel by representation of fact.

The test for unconscionability, takes many factors into account, including the behavior, state of mind and circumstances of the parties. Generally, the following eight factors are determinative:

  • 1. How the promise/representation and reliance upon it were induced
  • 2. The content of the promise/representation
  • 3. The relative knowledge of the parties
  • 4. The parties’ relative interest in the relevant activities in reliance
  • 5. The nature and context of the parties’ relationship
  • 6. The parties’ relative strength of position
  • 7. The history of the parties’ relationship
  • 8. The steps, if any, taken by the promissor/representor to ensure he has not caused preventable harm.

Estoppel by Representation of Fact:

Estoppel by representation of fact is a term coined by Spencer Bower. This species of estoppel is also referred to as "common law estoppel by representation" .

In The Law relating to Estoppel by Representation, estoppel by representation of fact as follows:

Where one person (’the representor’) has made a representation of fact to another person (’the representee’) in words or by acts or conduct, or (being under a duty to the representee to speak or act) by silence or inaction, with the intention (actual or presumptive) and with the result of inducing the representee on the faith of such representation to alter his position to his detriment, the representor, in any litigation which may afterwards take place between him and the representee, is estopped, as against the representee, from making, or attempting to establish by evidence, any averment substantially at variance with his former representation, if the representee at the proper time, and in proper manner, objects thereto.

A representation can be made by words or conduct. Although the representation must be clear and unambiguous, a representation can be inferred from silence where there is a duty to speak or from negligence where a duty of care has arisen. Under English law, estoppel by representation of fact usually acts as a defence, though it may act in support of a cause of action or counterclaim.

Equitable Estoppel :

The American doctrine of equitable estoppel is the same as the English estoppel by representation of fact:

The most comprehensive definition of equitable estoppel or estoppel in pais is that it is the principle by which a party who knows or should know the truth is absolutely precluded, both at law and in equity, from denying, or asserting the contrary of, any material fact which, by his words or conduct, affirmative or negative, intentionally or through culpable negligence, he has induced another, who was excusably ignorant of the true facts and who had a right to rely upon such words or conduct, to believe and act upon them thereby, as a consequence reasonably to be anticipated, changing his position in such a way that he would suffer injury if such denial or contrary assertion was allowed.

Proprietary Estoppel :

The traditional version of proprietary estoppel arises in negotiations affecting title to land. So if, one party represents that he or she is transferring an interest in land to another, but what is done has no legal effect, or merely promises at some time in the future to transfer land or an interest in land to another, and knows that the other party will spend money or otherwise act to his or her detriment in reliance on the supposed or promised transfer, an estoppel may arise.  A father promised a house to his son who took possession and spent a large sum of money improving the property. The father never actually transferred the house to the son. When his father died, the son claimed to be the equitable owner and the court ordered the testamentary trustees to convey the land to him.

Five elements have to be established before proprietary estoppel could operate:

  • 1. The plaintiff must have made a mistake as to his legal rights
  • 2. The plaintiff must have done some act of reliance
  • 3. The defendant, the possessor of a legal right, must know of the existence of his own right which is inconsistent with the right claimed by the plaintiff
  • 4. The defendant must know of the plaintiff’s mistaken belief
  • 5. The defendant must have encouraged the plaintiff in his act of reliance

Although proprietary estoppel was only traditionally available in disputes affecting title to real property, it has now gained limited acceptance in other areas of law. Proprietary estoppel is closely related to the doctrine of constructive trust.

The term "proprietary estoppel" is not used in American law, but the principle is part and parcel of the general doctrine of promissory estoppel.

Promissory Estoppel :

The doctrine of promissory estoppel prevents one party from withdrawing a promise made to a second party if the latter has reasonably relied on that promise and acted upon it.

Promissory Estoppel Requires:

  • (i) an unequivocal promise by words or conduct
  • (ii) evidence that there is a change in position of the promisee as a result of the promise (reliance but not necessarily to their detriment)
  • (iii) inequity if the promissor was to go back on the promise

Estoppel is "a shield not a sword",  it cannot be used as the basis of an action on its own. It also does not extinguish rights.

Estoppel is an equitable (as opposed to common law) construct and its application is therefore discretionary.

Promissory estoppel is not available when one party promises to accept a lesser sum in full payment of a debt, unless the debtor offers payment at an earlier date than was previously agreed.

American Law:

In the many jurisdictions of the United States, promissory estoppel is generally an alternative to consideration as a basis for enforcing a promise. It is also sometimes referred to as detrimental reliance.

The American Law Institute in 1932 included the principle of estoppel into the Restatement of Contracts, stating:

A promise which the promissor should reasonably expect to induce action or forbearance of a definite and substantial character on the part of the promisee and which does induce such action or forbearance is binding if injustice can be avoided only by enforcement of the promise. Restatement (Second) removed the requirement that the detriment be "substantial".

The distinction between promissory estoppel and equitable estoppel should be noted:

Equitable estoppel is distinct from promissory estoppel. Promissory estoppel involves a clear and definite promise, while equitable estoppel involves only representations and inducements. The representations at issue in promissory estoppel go to future intent, while equitable estoppel involves statement of past or present fact. It is also said that equitable estoppel lies in tort, while promissory estoppel lies in contract. The major distinction between equitable estoppel and promissory estoppel is that the former is available only as a defense, while promissory estoppel can be used as the basis of a cause of action for damages.

Other Estoppels:

Estoppel in Pais:

Estoppel in pais (literally "by act of notoriety", or "solemn formal act7quot;) is the historical root of common law estoppel by representation and equitable estoppel. The terms Estoppel in pais and equitable estoppel are used interchangeably in American law.

Estoppel by Convention:

Estoppel by convention in English law (also known as estoppel by agreement) occurs where two parties negotiate or operate a contract but make a mistake. If they share an assumption, belief or understanding of how the contract will be interpreted or what the legal effect will be, they are bound by that belief, assumption or understanding if:

  • (i) they both knew the other had the same belief
  • (ii) they both based their subsequent dealings on those beliefs

Some say that that estoppel by convention is not truly an estoppel in its own right, but merely an instance of reliance-based estoppel (estoppel by representation would be its most frequent form). Others see it is no more than an application of the rule of interpretation that, where words in a contract are ambiguous, you always interpret those words so as to give effect to the actual intentions of the parties even though that would not be the usual legal outcome.

Estoppel by Acquiescence:

Estoppel by acquiescence may arise when one person gives a legal warning to another based on some clearly asserted facts or legal principle, and the other does not respond within "a reasonable period of time". By acquiescing, the other person is generally considered to have lost the legal right to assert the contrary.

Estoppel by Deed:

Estoppel by deed is a rule of evidence arising from the status of a contract signed under seal, such agreements, called deeds, are more strictly enforced than ordinary contracts and the parties are expected to take greater care to verify the contents before signing them. Hence, once signed, all statements of fact (usually found in the opening recital which sets out the reason’s for making the deed) are conclusive evidence against the parties who are estopped from asserting otherwise.

Issue Estoppel:

Issue Estoppel or Res Judicata the civil law use of issue estoppel or res judicata (literally translated as "the fact has been decided") is relatively uncontroversial. It expresses a general public interest that the same issue should not be litigated more than once even when the parties are different. The criminal law application, called double jeopardy provides that a person should not be tried twice for the same offence.