Systems Theory:
the transdisciplinary study of the abstract organization of phenomena,
independent of their substance, type, or spatial or temporal scale of
existence. It investigates both the principles common to all complex
entities, and the (usually mathematical) models which can be used to
describe them.
See: http://pespmc1.vub.ac.be/SYSTHEOR.html

Systems theory or general systems theory or systemics is an interdisciplinary Interdisciplinarity article field which studies systems System article as a whole. Systems theory was founded by Ludwig von Bertalanffy Ludwig von Bertalanffy article , William Ross Ashby William Ross Ashby article and others between the 1940s 1940 article and the 1970s 1970 article on principles from physics Physics article , biology Biology article and engineering Engineering article and later grew into numerous fields including philosophy Philosophy article , sociology Sociology article , organizational theory Organizational theory article , management Management article , psychotherapy Psychotherapy article (within family systems therapy Family systems therapy article ) and economics Economics article among others. Cybernetics Cybernetics article is a related field, sometimes considered as a part of systems theory.
See http://www.definition-info.com/Systemics.html