The invention relates to the use of block copolymers as leveling agents for surface coatings, having a weight-average molecular weight of from 1000 to 100000. The leveling agent is a linear or branched block copolymer composed of a polysiloxane block and one or more blocks prepared from ethylenically unsaturated monomers by controlled free-radical addition polymerization.The invention also relates to coating compositions which comprise the leveling agent.