Second generation gravitational wave detectors require high power lasers with several 100 W of output power and with very low temporal and spatial fluctuations. In this paper we discuss possible setups to achieve high laser power and describe a 200 W prestabilized laser system (PSL). The PSL noise requirements for advanced gravitational wave detectors will be discussed in general and the stabilization scheme proposed for the Advanced LIGO PSL will be described. Special emphasis will be given to the most demanding power stabilization requiremets and new results (RIN ≤ 4 × 10−9 / √Hz) will be presented.