In this article of the Doctor of Law, associate professor of the Department «Interpol» of the Ural Federal University named after the first president of Russia B.N. Yeltsin S.M. Troshina (e-mail: troshina-svetlana63@mail.ru) legal differences between the unconcluded and void contract, as well as their legal consequences, are given. Unjust enrichment and void contracts are regarded in connection with these issues.