Scanning tunneling microscopy (STM) is used to characterize partial monolayers of C 60 , C 70 , and C 84 adsorbed on the Au(111) surface at room temperature and under ambient conditions. A high degree of structural polymorphism is observed for monolayers of each of these fullerenes. For C 60 , three lattice packings are observed, including a previously unreported 7×7R21.8° structure that is stabilized by adjacent surface step defects. For C 70 , two lattice packings are observed, and analysis of molecular features in STM images allows molecular binding geometry to be determined. In one of the two observed lattice structures, C 70 molecules align their long axis along the surface normal, while in the other, molecules align parallel to the surface and along a gold lattice direction. The parallel geometry is also preferred for isolated and loosely packed molecules on the surface. C 84 exhibits a large number of lattice orientations and no long-range order, and likely binds incommensurately on Au(111). Time series of images of partial C 70 monolayers show progressive surface modification as a result of perturbation by the STM tip; this is in contrast to the behavior of C 60 , where alterations in surface structure at room temperature are thermally driven.