Abstract
Ludwig von Bertalanffy was a key figure in the advancement of theoretical biology. His early considerations already led him to recognize the necessity of considering the organism as a system, as an organization of parts and processes. He termed the resulting research program organismic biology, which he extended to all basic questions of biology and almost all areas of biology, hence also to the theory of evolution. This article begins by outlining the rather unknown (because often written in German) research of Bertalanffy in the field of theoretical biology. The basics of the organismic approach are then described. This is followed by Bertalanffy's considerations on the theory of evolution, in which he used methods from theoretical biology and then introduced his own, organismic, view on evolution, leading to the demand for finding laws of evolution. Finally, his view on the concept of homology is presented.