We present a selection of results obtained from Monte Carlo simulations of systems of alkyl thiol molecules chemisorbed on a gold surface. Topics discussed include the nature of the orientational, translational and conformational disorder within the monolayer and its dependence on the assumed potential model; the structural relaxation of a monolayer in response to the approach of a force-microscope tip; the tendency for different species to segregate in mixed systems consisting of alkyl thiols of different lengths; and the relative merits of the Monte Carlo and molecular dynamics methods of simulation.