Ništetni pravni poslovi su oni koji ne proizvode pravne učinke koje bi, da su valjani, trebali proizvesti. Neki od razloga ništetnosti su: poslovna nesposobnost stranaka, nevaljanost i nesuglasnost očitovanja volje (školski primjer, šala, nesporazum, prividan ugovor), nemogućnost, nedopustivost, neodređenost i neodredivost činidbe te nedopuštenost pobude za sklapanje ugovora. Pobojan ugovor nastaje kad ga je sklopila ograničeno poslovno sposobna osoba, kad je pri njegovu sklapanju bilo mana u pogledu volje. Poništenje pobojnog pravnog posla može se tražiti u roku od jedne do tri godine. Poništenje ništetnog ugovora nikada ne zastarjeva.

A contract is valid when the agreement is consensual, legal, backed up with a promise of consideration, and is executed by two adult parties who are in sound mind. A contract becomes voidable when; mutual mistakes on behalf of both parties occur, a party has been coerced or threatened into signing the agreement or a party to the contract is able to dominate the will of the other party, a party to the contract is not of sound mind or is not mentally competent, the terms of the contract had been breached or the contract is fraudulent through the omission or through the falsifying of facts or information or with the intention to not carry out the promise in the contract. An voidable contract is created when a person with restricted business capacity is a party to the contract. Cancellation of a contract may be sought within one to three years. For non binding contracts no party shall have any legal rights or obligations with respect to any other party for the cancellation of a non binding contract.