Abstract: The paper considers the main models of a third party’s impact on the dynamics of a civil debt and classifies them. The classification is based on a combined criterion including two elements: the first element consists in the third party of the debt; the second element reflects the peculiarities of the interests of the participants to the debt relationship, which is implemented with the involvement of the third party to the dynamics of the civil debt. The author detects two basic models of the third party’s impact on the dynamics of the civil debt: I model – the participation of the third party in performing the obligation on the side of the debtor; II model – the participation of the third party on the side of the lender. The research methodology is based on general scientific (descriptive, logical, system-structural, historical, linguistic methods, analysis and synthesis) and specific methods of jurisprudence (historical-legal, formal-legal, comparative-legal and technical-legal methods). The author concludes that the involvement of a third party usually leads to the transformation of some attribute of the proper performance of the obligation, for example, a place, a person, a subject or a time period. Thus, a contract, based on the model with the benefit of a third party, contains the transformation of such attributes of the proper performance as a proper person and a proper place. The peculiarities of involvement of a third person in the dynamics of an obligation depend on the character of the obligation: the third person can participate in the dynamics of both contractual and non-contractual obligations, including improper profit, delict and maintenance obligation. It’s important to understand that the involvement of the third party on the side of a debtor or a lender doesn’t form active or passive plurality of persons in an obligation.