A lot of national and foreign researchers attempted to examine the theoretical grounds of the challenging of the transactions under the bankruptcy legislation. Thus, tort and quasi-delictual theory, the theory of executive power of the judgment, the theory of the judicial lien and legal theory have been developed. However, until now there hasn’t been developed a unified approach to understanding of the question of what is the basis of the creditor’s right to demand recognition of the debtor’s invalid transaction committed by itself with a third party, in respect of which insolvency (bankruptcy) case has been initiated. This paper analyzes the main concepts developed in support of the rights of the creditor and assesses their strengths and weaknesses. The study and its findings formulated on the basis of the former have allowed the author to offer his own opinion based on challenging the debtor´s transactions. The author reveals the purpose of legal regulation of invalidity of transactions the debtor committed to them on the eve of bankruptcy. This purpose is to protect the rights and property interests of both the debtor and the creditors, as well as is the formal (violation of the law) and material (violation of the property rights of the debtor and its creditors) base to contest the transactions.