What legal doctrine allows a promise to be enforced even without consideration?

The legal doctrine that can enforce a promise even without consideration is promissory estoppel.

Ordinary contract law generally requires consideration: each side must give or promise something of legal value. Promissory estoppel is an equitable exception that may apply when one party makes a clear promise, reasonably expects reliance, and the other party actually relies on it to their detriment. Enforcement must also be necessary to avoid injustice.

The doctrine is often used when negotiations or informal commitments fall short of a traditional contract. A person might spend money, give up another opportunity, or change position because of a promise, only to suffer loss when the promise is withdrawn. Courts may award reliance damages or, in some circumstances, provide another appropriate remedy.

A classic American example is Hoffman v. Red Owl Stores, a 1965 Wisconsin Supreme Court case involving reliance on assurances about opening a grocery store. Promissory estoppel is not the same as equitable estoppel: equitable estoppel usually prevents a party from contradicting a representation after another person relied on it, while promissory estoppel centers on reliance on a promise.