The present status of research in the field of macromolecules/transition metal complexes is critically reviewed on the basis of selected examples both from the authors′ laboratories and other laboratories around the world. The substantial lack of inertness of the polymeric ligand (the polymer effect) is examined and shown to occur in most cases during preparation of the macromolecule/transition metal complex as well as during its catalytic use. This behavior is attributed and confirmed as due to the polydentate ligand character of the macromolecules and to the effect of physical and chemical parameters which can be varied over large ranges. Future work is duscussed for the development of the field in suitable directions.