Abstract: The subject of the article is the examination of evolution of the institution of accessory obligations and its gradual “infiltration” into Russian law. The author reviews the genesis of the category of “accessority” in Roman law, within the framework of which its initial formula “the validity of the accessory legal relationship is predetermined by the validity of the basic legal relationship" gained widespread. Description is given to the peculiarities of evolution of accessority in Russian law. In civil law of pre-revolutionary Russia, accessority was being neglected for a long time. In the Soviet period, the identification of the terms “security obligation” and “accessory obligation” established in civil science. Currently, in Russian law, the concept of “accessority” is identified with the security obligation. The conclusion is made on versatility of the category of “accessority”. In the course of the development of law, the concept of accessory obligations undergone significant changes – from perception of accessority as a certain obligation that ensures the repayment of debt and the transfer of “belonging” to the sold goods towards its identification with security obligations as a whole. With time, the opinion that accessority is attributed to different types of obligations with own features and specifics, has established in the legal doctrine. The relevance of the selected topic is defined by a range of problematic questions, which have not been previously covered in Russian civil science. Thus, the legislation of the Russian Federation does not contain a legal definition of the concept of accessory obligations. The civil law doctrine also does not have a unanimity of opinion on the matter. The authors assume that the established situation, namely in the context of the civil legislation that has been fundamentally reformed in 2012 – 2015, does not contribute to unified understanding of the essence of accessory obligations and optimization of their doctrinal interpretation.