The growing demands on the performance of magnetron sputter sources require the improvement of existing equipment, the realization of new ideas and the more detailed understanding of the sputter process physics. In this paper the possibilities and methods of magnetron preoptimization by numerical modelling are discussed regarding various model tools. The primary problem in magnetron development is to achieve a good thickness uniformity of the deposited layer on the substrate. Therefore the optimization of the erosion track and deposition geometry is essential. The erosion track location is determined by the magnetic field. Model calculations of film thickness distributions and magnetic fields are reported and compared with experimental measurements with the double ring magnetron DRM 250. A Monte-Carlo model for the motion of charged particles in electric and magnetic fields gives a qualitative and quantitative image of the sputter process in the target vicinity and of the charged particle stream on to the substrate. These results are helpful for the further optimization of target geometry and electric and magnetic field configuration.