System identification allows fast and accurate modelling of magnetic bearing systems. It makes statis measurement of bearing characteristics and modal analysis of flexible rotors obsolete. This eliminates the need for the related expensive measurement equipment, and result in a substantial reduction in the time required for commissioning. Moreover, the achieved control performance can be improved. idntification of magnetic bearings must be tailored to the controller. Strategies for this are proposed. Experimental results for various set-ups are presented.