A novel concept for the generation of molecularly thin polymer layers attached to a solid surface is described. In contrast to commonly used techniques, where functional groups of the polymers are reacted with appropriate sites on the surfaces of a substrate the polymer layers are formed in situ by using self-assembled monolayers of an initiator. As an example, the formation of polystyrene monolayers terminally attached to silicon oxide surfaces through radical chain polymerization which has been started by a self-assembled monolayer of an azo initiator is described. The thickness of the attached polymer films can be adjusted over a wide range up to values of several hundred nanometers by variation of polymerization parameters such as temperature and azo conversion. When suitable conditions are chosen, monolayers with thicknesses inaccessible by other techniques of preparation can be obtained.