We have used an ultra-high-vacuum (UHV) scanning tunnelling microscope (STM) to image molecules adsorbed on a Si(111) surface. At low coverage ( monolayers) molecules are adsorbed at random sites. For coverages close to a monolayer they are partially ordered in a hexagonal arrangement. Second- and higher-layer islands, in which the molecules are clearly resolved, are observed at higher coverage. These islands may be desorbed by annealing in the range , leaving an Si surface terminated by a monolayer. This surface is stable to exposure to air and immersion in water. In addition, recent work on manipulation of molecules at various coverages is reviewed and results relating to tip alignment in UHV are discussed.