The interaction of simple diatomic molecules (CO, NO, H₂, N₂) with transition metal surfaces may lead to breaking and making chemical bonds and trigger important surface catalyzed reactions. The specific behavior of each transition metal considered, the influence of the structure of the surface, and the bonding and coordination of the molecules are analyzed. A molecular orbital description of adsorption and dissociation of simple molecules on transition metal surfaces is presented. Charge transfer analysis is used to describe the principal features of the electronic interaction between adsorbed molecule and metal. The predissociative tilted state of CO on Fe(100) and Cr(100) is described using ab intio Hartree Fock results and resonating valence bond theory.