A detailed analysis of the valence molecular orbitals (MO) in Cr(CO)6, Mo(CO)6, and W(CO)6is presented. A generalized bonding scheme, which includes participation of metal p electrons in the metal–ligand bond, emerges from our results. The metal p electrons are also responsible for effecting mixings between different sets of carbonyl 5σ and 1π orbitals. In these hexacarbonyls, this ‘‘σ’’+‘‘π’’ metal–ligand bonding contribution is quantitatively as significant as the well known σ donation and π‐back‐donation components. The MO’s obtained with the Dirac scattered‐wave (DSW) method are also used to determine the importance of relativistic effects in this series. The DSW results show that even in W(CO)6, relativistic effects are qualitatively unimportant. Extensive comparisons with existing theoretical and experimental data are made for both ground‐state and transition‐state calculations.