His paper explored the invalidity of illegal transactions of business entities in the context of the principle of legality. In Russian judicial practice and doctrine, the invalidity of illegal transactions of business entities is usually considered in terms of the application of the legal grounds for invalidity to particular transactions. Therefore, the authors focus on these grounds and the legal consequences related to them. The problems related to the subject and the normative role of the rules governing the invalidity of transactions are not less important in the Russian legal system. His paper explored the invalidity of illegal transactions of business entities in the context of the principle of legality. In Russian judicial practice and doctrine, the invalidity of illegal transactions of business entities is usually considered in terms of the application of the legal grounds for invalidity to particular transactions. Therefore, the authors focus on these grounds and the legal consequences related to them. The problems related to the subject and the normative role of the rules governing the invalidity of transactions are not less important in the Russian legal system. His paper explored the invalidity of illegal transactions of business entities in the context of the principle of legality. In Russian judicial practice and doctrine, the invalidity of illegal transactions of business entities is usually considered in terms of the application of the legal grounds for invalidity to particular transactions. Therefore, the authors focus on these grounds and the legal consequences related to them. The problems related to the subject and the normative role of the rules governing the invalidity of transactions are not less important in the Russian legal system. His paper explored the invalidity of illegal transactions of business entities in the context of the principle of legality. In Russian judicial practice and doctrine, the invalidity of illegal transactions of business entities is usually considered in terms of the application of the legal grounds for invalidity to particular transactions. Therefore, the authors focus on these grounds and the legal consequences related to them. The problems related to the subject and the normative role of the rules governing the invalidity of transactions are not less important in the Russian legal system