Systems thinking is an important factor in solving global problems.
The twentieth-century has witnessed the development of a systems paradigm and different spheres of systems knowledge. However, further development of systems thinking necessitates overcoming the contradictions between different schools and unifying them into a single systems conception. With this in mind, systems problems are examined in light of the theory of knowledge. It is suggested that the gnosiological definition of the notion 'system' should be used as a basis for a single approach. An analysis of the concept 'system' leads to a logically well-structured conception of system.