The recent development of temperature controlled scanning tunneling microscopy opened the door to a fascinating new world on the nanometer scale. The atomic scale information obtained provides unprecedented insight into the kinetics of surface phenomena such as epitaxial growth or chemisorption. In particular, a rich variety of surface structures could be observed, whose morphologies are determined by the self-assembly of the adsorbed particles. Temperature control allows for detailed investigations of the microscopic processes which are at the origin of the self-assembly. Some illustrative examples are discussed, particularly the initial stages in heteroepitaxial growth of metals (Ag, Cu) On fcc Single crystal metal substrates with different symmetry (Pd(110), Pt(111), Ni(100)) with emphasis on the island shapes as well as a novel pattern formation in dissociative adsorption of molecular oxygen on Pt(111).