Systems theory is a transdisciplinary study of systems, which are cohesive groups of interrelated, interdependent components that can be natural or human-made. The key concept of systems theory is that the whole is greater than the sum of its parts, regardless of which discipline it is being applied to. The goals of systems theory are to model a systems dynamics, constraints, conditions, and relations, and to elucidate principles that can be discerned and applied to other systems at every level of nesting, and in a wide range of fields for achieving optimized equifinality.

Systems theory is a way of elaborating increasingly complex systems across a continuum that encompasses the person-in-environment. It distinguishes dynamic or active systems from static or passive systems. Active systems are activity structures or components that interact in behaviors and processes or interrelate through formal contextual boundary conditions (attractors). Passive systems are structures and components that are being processed.

Systems theory is frequently identified with cybernetics and control theory, but this is incorrect. Cybernetics as the theory of control mechanisms in technology and nature is founded on the concepts of information and feedback, but as part of a general theory of systems.

Systems theory is applied in many fields, including social work, psychology, sociology, and social science. When applied to social work, systems theory enables professionals to look holistically at a clients conditions and environmental factors. It provides a powerful method for the description of homeostatic systems, that is, systems in which feedback-controlled regulation processes occur. Systems theory plays a key role in the advancement of society by looking at all the moving parts to have a greater understanding of the whole and how it works.