Abstract: This article examines the voluntariness as the key principle that lies in the foundation of establishment on the relations between the member-states in the context of creating the transnational formation, as well as the emerging due to implementation of the main goals. The author formulates the notion of voluntariness; reviews the consolidation of this term in the normative legal acts of domestic legislation and international legal acts ratified in the Russian Federation, as well as decisions and decrees of the Constitutional Court of the Russian Federation. The principle of voluntariness is subject to a more detailed research through the prism of international relations of the Russian Federation, as one of the fundamental principles that define the partial delegation of authorities of the Russian Federation to a certain transnational formation. The author meticulously analyses the consolidation, realization, and effect of the principle of voluntariness in various branches of the law. Operation of the principle of voluntariness is applied to the member-states, authorities, officers, subjects of international law that incurred obligations for international agreements before the transnational formation. The discussed principle also lies in the foundation of the organizational relations (establishment of transnational formation, entering/exiting the membership), relations between the member-states regarding the realization of the undertaken responsibilities, exercise of powers by the authorities, employment relationship and foreign relations pertaining to the international activity of transnational formation.