It is a truism that ligands play a dominant role in homogeneous transition metal based catalysis. However, finding and predicting the right ligand. to a large extent, is still determined by trial and error. To practise homogeneous catalysis a better concept of general applicability is needed. The coordination geometry seems to play an important role. Bidentate and tridentate ligands are presented postulating that a distinguished coordination geometry is required for catalysis to occur. Monodentate ligands based on trivalent phosphorus have been studied extensively, whereas oxygen-, nitrogen- and sulphur-containing ligands have been neglected compared to phosphorus. Based on our research carried out over many years a conceptual view by the author is Given presenting O-O, S-O. N-O, N-N-N, P-N-P and S-N-S ligands and elucidating to their catalytic behaviour. It is recommended for future research to pay more attention to the coordination geometry and to bio-inspired ligands. (C) 2004 Elsevier B.V. All rights reserved.