One of the main design goals of the MAGIC telescopes is the very fast repositioning in case of e.g. GRB alarms, implying a low weight of the reflector dish. This is accomplished by using a space frame made of carbon fiber epoxy tubes, resulting in a strong but not very rigid support structure. Therefore it is necessary to readjust the individual mirror tiles to correct for deformations of the dish under varying gravitational load while tracking an object. We will present the concept of the Active Mirror Control (AMC) as implemented in the MAGIC and MAGIC-II telescope and the actual performance reached. Additionally, we will show that also telescopes with stiff structure can benefit from using an AMC.