In a general sense, Promissory Estoppel is a legal doctrine used in American law, which allows a party to recover on a promise, even if the promise was made without a formal consideration. In essence, a Promissory Estoppel prevents an individual from arguing that an underlying promise offered should not be upheld.

In addition, a Promissory Estoppel requires that a reliance on the promise was deemed reasonable and that the individual attempting to enforce the promise actually relied on the promise to his or her detriment. As is common with numerous forms of legality issues, the precise legal requirements needed to enact Promissory Estoppel may vary between jurisdictions within the United States.

A common example of Promissory Estoppel is where an employer offers an oral promise to pay an employee a monthly amount for the remainder of the individual’s retirement. If the employee relies on the promise and subsequently retires, the employer will likely be estopped, based on the principle of a promissory estoppel, from reneging on this promise to offer the monthly retirement payment.

In a typical case of a promise or a contract, the law requires that a party receive consideration for the agreement. Consideration refers to a valuable asset that is exchanged between the two parties and the time of the agreement or the promise was made. Consideration can take the form of an asset, the exchange of monies, or the promise to refrain from doing something. Regardless of the form of consideration required in a contract, a consideration is needed in order to make an agreement or promise legally enforceable.

That being said, because the court system aims to achieve fairness, a legal forum will apply the doctrine of promissory estoppel in situations where a consideration is made. Even if an enforceable contract is not generated, the law may enforce the promise if a reasonable reliance and detriment are proven.

A promissory estoppel relies on a promise, while the doctrine of estoppel relies on a statement of fact. As a result of this foundational difference, the two doctrines complicate contractual agreements or the statement of a promise. Even if an agreement is not based on a formal consideration and even if promissory estoppel is not enforceable, because the situation did not include a promise, a court system can still enforce the “agreement” as a means to promote fairness.

This somewhat loose interpretation of promissory estoppel enables the court to impose obligations on the parties through the delivery of a quasi-contract—a doctrine that implied in law.