After a general introduction to and a brief historical survey of the development of systems approach the autors try to explore the significante of the system concept for clinical psychiatry as a potential tool for reconceptualizing the theories about the complex phenomena in psychiatry. According to their definition a system represents a whole as an organized set of independent components. They stress the importante of Boulding's classification of systems as a starting point for application of the system concept in psychiatry. In this way one can avoid one-sidedness in theorizing about phenomena as 'group' or 'family'. Moreover, till psychiatrical system models have been developed that can be formalized adequately, in psychiatry the term system approach can only be used to denote a way of thinking, a 'philosophy'.