In this paper we demonstrate how low energy electron microscopy can be used to study in situ, and in real time, the growth of thin films on single-crystal surfaces. By studying the growth of Ge and Ag on both the clean and the Sb-terminated Si(lll) surface we show how nucleation, growth, island formation, island shapes, thermal stability and the formation of dislocations in the grown films may be observed. Pre-adsorption of Sb strongly modifies the growth of Ge and Ag films on Si(lll), leading to more uniform coverage and smoother films in both cases.