estoppel

Estoppel is a legal principle that prevents a party from asserting a claim or fact that is inconsistent with that party’s previous representations, conduct, or legal status if another party has relied on them to their detriment. It functions to promote fairness by enforcing consistency and discouraging inequitable behavior.

Promissory estoppel arises when a promise, even in the absence of consideration, leads another to rely on it to their detriment. The typical elements include a clear or definite promise, reasonable reliance on the promise, reliance that leads to a substantial change of position or detriment, and a result that would be unjust if the promise were not honored.

Collateral estoppel, also known as issue preclusion, prevents re-litigation of an issue that was actually litigated and essential to a prior final judgment. It requires suitable identity of issues and parties, and that the prior adjudication was final and on the merits.

Equitable estoppel, or estoppel by conduct or representation, bars a party from taking a position inconsistent with their previous conduct when another party relied on that conduct to their detriment. In property law, proprietary estoppel can arise when someone is led to believe they will obtain an interest in land and acts to their detriment, and the other party cannot later deny the interest.

Judicial estoppel prevents a party from adopting a contrary position in a subsequent legal proceeding if they previously took a contradictory position in a prior proceeding, in order to preserve the integrity of the judicial process.

Estoppel is rooted in equity and is generally discretionary, used to prevent injustice rather than to create rights. It is most developed in common law jurisdictions, with analogous concepts appearing in other legal systems.