The invention relates to a method for monitoring the condition of rotor blades for wind turbines. It is therefore the object of the invention to increase the accuracy of the monitoring of the condition of rotor blades of wind turbines and to allow a localization of faults or defects and their exact description. In the method in accordance with the invention, eigenvibrations of a rotor blade occurring globally at the rotor blade and locally guided elastic waves are permanently detected with time and spatial resolution using a sensor network and actuator network attached to the rotor blade or using a network arrangement of ultrasound transducers. In addition, elastic waves which are guided periodically at predefinable time intervals and which are respectively emitted by an actuator or ultrasound transducer and detected by sensors or ultrasound transducers are in so doing inspected for variations of the emitted waves.