The purpose of this study is to reveal the matter of legal practice of institutes of transactions accomplished under influence of error and performance of contractual obligations in a case of change of circumstances. In the first chapter author provides the conception of contracts accomplished under influence of error, classification into mutual and unilateral mistakes, separate bases that misleads a person, also legal consequences of anullement of such a transactions. In the second chapter author provides the conception of performance of contractual obligations in a case of change of circumstances, analyses connection between aforementioned institute and frustration and legal consequences of anullement or modifying of contract in a case of change of circumstances. The last chapter compares institutes of anullement of transactions accomplished under influence of error and performance of contractual obligations in a case of change of circumstances.