Systems theory or systemics is an interdisciplinary field which studies relationships of systems as a whole. Modern systems theory was founded by Ludwig von Bertalanffy, William Ross Ashby and others between the 1940s and the 1970s on principles from philosophy, physics, biology and engineering and later grew into numerous fields including philosophy, sociology, organizational theory, management, psychotherapy (within family systems therapy) and economics among others. Cybernetics is a closely related field. In recent times complex systems has increasingly been used as a synonym.

Overview:
Systems theory focuses on complexity and interdependence of relationships. A system is composed of regularly interacting or interdependent groups of activities/parts that form the emergent whole.

Part of systems theory, system dynamics is a method for understanding the dynamic behavior of complex systems. The basis of the method is the recognition that the structure of any system -- the many circular, interlocking, sometimes time-delayed relationships among its components -- is often just as important in determining its behavior as the individual components themselves. Examples are chaos theory and social dynamics.

Systems theory has also been developed within sociology. The most notable scientist in this area is Niklas Luhmann. The systems framework is also fundamental to organizational theory as organizations are dynamic living entities that are goal-oriented. The systems approach to organizations relies heavily upon achieving negative entropy through openness and feedback.

In recent years, the field of systems thinking has been developed to provide techniques for studying systems in holistic ways to supplement more traditional reductionistic methods. In this more recent tradition, systems theory is considered by some as a humanistic extension of the natural sciences.

General systems theory as an Objective of Systemics:
Early systems theorists aimed at finding a General systems theory that could explain all systems in all fields of science. The term goes back to Bertalanffys basic work 'General Systems Theory'. Sociologists like Niklas Luhmann also worked towards a general systems theory, but as of today no systems theory can live up to this claim. However, there are general system principles which are found in all systems. For example, every system is an interaction of elements manifesting as a whole.

History:
Subjects like complexity, self-organization, connectionism and adaptive systems had already been studied in the 1940s and 1950s, in fields like cybernetics through researchers like Norbert Wiener, William Ross Ashby, John von Neumann and Heinz Von Foerster. They only lacked the right tools, and tackled complex systems with mathematics, pencil and paper. John von Neumann discovered cellular automata and self-reproducing systems without computers, with only pencil and paper. Aleksandr Lyapunov and Jules Henri Poincaré worked on the foundations of chaos theory without any computer at all.

All of the "C"-Theories below - cybernetics, catastrophe theory, chaos theory,... - have the common goal to explain complex systems which consist of a large number of mutually interacting and interwoven parts. Cellular automata (CA), neural networks (NN), artificial intelligence (AI), and artificial life (ALife) are related fields, but they do not try to describe general complex systems. The best context to compare the different "C"-Theories about complex systems is historical, which emphasizes different tools and methodologies, from pure mathematics in the beginning to pure computer science now. Since the beginning of chaos theory when Edward Lorenz accidentally discovered a strange attractor with his computer, computers have become an indispensable source of information. One could not imagine the study of complex systems without computers today.