Systems theory is the interdisciplinary study of systems in general, with the goal of discovering patterns and elucidating principles that can be discerned from, and applied to, all types of systems at all nesting levels in all fields of research. Systems theory can reasonably be considered a specialization of systems thinking or as the goal output of systems science and systems engineering, with an emphasis on generality useful across a broad range of systems (versus the particular models of individual fields).

A central topic of systems theory is self-regulating systems, i.e. systems self-correcting through feedback. Self-regulating systems are found in nature, including the physiological systems of our body, in local and global ecosystems, and in climate—and in human learning processes (from the individual on up through international organizations like the UN).