The bond-energy bond-order (BEBO) model of chemisorption allows an estimate to be made of the interaction energy between a gaseous specie and a solid surface as a function of either bond length or bond order, i.e., the length or order of either the gas-surface bond being formed or the bond of the gaseous molecule being broken. The relationship between bond energy and either bond length or bond order is deduced from spectroscopic correlations for gaseous molecules, and a linear relationship between bond energy and bond order is assumed for the surface-adsorbate interaction. The geometry of the surface orbitals is taken to be that predicted by the crystal field model. The model allows a prediction of several relevant quantities in gas-surface interactions, namely: (1) binding energies for molecular adsorbed species, (2) binding energies for atomically adsorbed species, (3) activation energies to chemisorption, and (4) activation energies to dissociative chemisorption. The model is illustrated for the adsorption of H2, CO, NO and O2 on Pt, W and Ni surfaces.