A contract is null and void when it can no longer be legally enforced. If one party to the contract gives an indication that it is unable to hold up its end, the other party may claim an anticipatory breach of contract. If the agreement is unconscionable or grossly unfair to one party, or one party commits fraud, the contract may be void.
An agreement may also be void if one party is incompetent or a minor and unable to enter a legal agreement, a bilateral mistake is made, it involves restraint of legal proceedings, it is an agreement with uncertain terms, it is a wager or it involves impossible acts. For example, if one's house burns down before a contractor is able to repair the roof, the contract is voided, as the terms have become impossible to fulfill. There may be a time frame in which a contract may be voided, though there is no universal grace period. For example, mortgage refinance transactions carry a three-day right of rescission. If one party lies to the other about key issues in the contract, the other party may not only void the contract but sue for anything paid or lost in addition to punitive damages.