The three volumes comprising "Nature, Cognition and System" present a representative collection of reports on current research in the major topics of system theory and cybernetics as applied to the two main classes of systems, that is the natural and cognitive systems. The contributions present such time-honoured and controversial issues of the "nature-cognition-system connection" which in principle and in fact form the very subject-matter of the current "sciences of complexity". In the present volume Niels Borh's seminal ideal of "complementarity" has been chosen as the hinge around which these discussions, critical appraisals, alternative views and applications, both orthodox and non-orthodox, have taken place. This pivotal notion seems to exert an appeal not only upon the strictly technical of disciplinary aspects of quantum physics, but also upon the wider epistemological understanding, which is based on the role and nature of language for measurement processes, thet Bohr himself seemed to apply to subjects other than physics and which later might turn out to be of primary importance for an explanation in genuine system-scientific context. Volume two is organized into three parts. The first part contains contributions which have been written in the spirit of the Copenhagen Interpretation. The second one contains those with a pronounced critical mood towards the orthodox theory, including the discussions among others of the problematic issues of physics and cognitive science. The third part is dedicated to the discussions of this complex "nature-cognition-system connection" from the non-orthodox point of view. This text should be useful to researchers, practitioners, teachers and students of the variety of disciplines making up modern system theory, cybernetics and cognitive science.