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A promissory estoppel has occurred if

• one party to a Contract indicates unequivocally to the other that he (the first party) will not insist on his full rights under the contract, and
• the party so benefited acts on the promise by adopting a course of action that he would not otherwise have taken, and
• it would be inequitable to allow the promisor to renege on the promise and insist on his full rights.

The courts might act to prevent the promisor going back on his promise and claiming his full rights. This issue arises sometimes in disputes over contracts, and may be used to imply the existence of a contract where there is insufficient Consideration.