The author examines main directions for the development of the doctrine of third parties in the sources of Russian Civil Law. The article determines mandatory and optional legal forms of the third party's participation in a contractual relationship. During the common law dominance, such a mandatory form of third party's participation emerged as verification of the will of the parties to the contract. By the XVII century, a procedure for public verification of transactions by third parties had been established. Optional participation of a third person in a contractual relationship was permitted under Prostrannaya redaktsiya Russkoy Pravdy [The Expanded Version of Russkaya Pravda] when testator's obligations were transferred to third-parties, i.e. his heirs. Pskovskaya sudnaya gramota [The Pskov Court Charter] mentions such a way of enforcing the fulfillment of obligations as a third person performing the contract as a guarantor (surety). Legislation of the 18th century provides for the participation of a third person as a voluntary representative. In business practice of the 19th century, it became possible to conclude contracts in favor of a third person, as well as to give to the third person the opportunity to act as a pledger who is not a debtor under the main obligation. The Civil Code of the Russian Federation of 1964 established the possibility of the third party's participation as a guarantor. Federal Law No. 100-FZ of 07 May 2013 enshrined the provision containing a general rule with respect of the consent of a third party to the transaction in the Civil Code of 1994.