Promissory estoppel is an equitable theory of recovery that permits enforcement of a promise when one or more elements necessary to create an enforceable contract are missing.

The elements of promissory estoppel are generally: (1) a promise; (2) foreseeability of reliance by the promisor; (3) substantial and reasonable reliance by the promisee to its detriment; and (4) enforcing the promise is necessary to avoid injustice.

In New York, promissory estoppel serves as a legal remedy that allows a party to enforce a promise even when a formal contract does not exist or when certain elements of a contract are missing. The doctrine is based on principles of equity and fairness, aiming to prevent injustice that would result from the promisor's failure to fulfill a promise that led the promisee to reasonably rely on that promise to their detriment. The key elements required to establish a claim of promissory estoppel in New York include: (1) a clear and unambiguous promise, (2) a reasonable expectation by the promisor that the promisee will rely on the promise, (3) actual and reasonable reliance by the promisee on the promise, and (4) a detriment suffered by the promisee as a result of their reliance. If these elements are met, New York courts may enforce the promise to the extent necessary to remedy the harm caused by the reliance. This doctrine is particularly important in situations where formal contract requirements are not satisfied, but where parties have acted in reliance on promises made.