The adsorption of thiolates on Au surfaces employing density-functional-theory calculations has been studied. The dissociative chemisorption of dimethyl disulfide (CH(3)S-SCH(3)) on 14 different Au(hkl) is used as a model system. We discuss trends on adsorption energies, bond lengths, and bond angles as the surface structure changes, considering every possible Au(hkl) with h, k, l ≤ 3 plus the kinked Au(421). Methanethiolate (CH(3)S-) prefers adsorption on bridge sites on all surfaces considered; hollow and on top sites are highly unfavourable. The interface tensions for Au(hkl)-thiolate interfaces is determined at low coverage. Using the interface tensions in a Wulff construction method, we construct atomistic models for the equilibrium shape of large thiolate-covered gold nanoparticles. Gold atoms in a nanoparticle change their equilibrium positions upon adsorption of thiolates towards shapes of higher sphericity and higher concentration of step-edge atoms.