Summary: The article suggests defining the content of the concept of "pension system". The essence of the pension system as a complex open organizational integrity is substantiated. Features the origin and functioning of the subsystems of the pension system of Ukraine are considered, taking into account the manifestation of principles, regularities, hypotheses of the general theory of systems. A model of the pension system was developed at the present stage of development of the Ukrainian society.
Key words: pension system, pension insurance, pension, reforming of the pension system of Ukraine, subsystems of the pension system, general theory of systems.