Promissory estoppel prevents the State or its officers from reneging on clear promises when reliance produces injustice. The doctrine of promissory estoppel binds a promisor who makes a clear promise intended to be relied upon and where such reliance causes prejudice, but it does not apply to sovereign legislative, executive or governmental functions; unauthorized acts by officers are governed by ultra vires, while representations made within authority under a scheme may be enforced where reliance has altered a party's position, subject to limited exceptions for executive necessity or overriding public interest.