This paper is concerned with various factors which may influence the chemisorption bond on metal surfaces. Its localized character is demonstrated by a comparison of the cluster compound Rh6(CO)16 with CO adsorbed on an extended Pd(111) surface. The influence of the position of the adsorbed particle within the unit cell of the substrate lattice is discussed with the system CO/Pt(111). Distortions of the perfect periodicity of low-index single-crystal planes may act ’’active sites’’ whose atomistic properties are illustrated by the interaction of hydrogen with ’’flat’’ and stepped Pt(111) surfaces. Direct or indirect interactions between neighboring adsorbed particles responsible for their geometric configuration on the surface and may cause variations of the bond energies and of the electonic properties as outlined by several examples.