A process for preparing aqueous polymer dispersions is described comprising the steps: (a) polymerizing at least one ethylenically unsaturated monomer having one or more ethylenically unsaturated groups and/or at least one ethylenically unsaturated surfactant monomer by free-radical aqueous emulsion polymerization to provide a first polymer; and (b) further polymerizing, in one or more successive polymerization stages, one or more monomers selected from ethylenically unsaturated monomers and/or ethylenically unsaturated surfactant monomers by free-radical polymerization in aqueous dispersion of the first polymer.