The technological development of wind energy plants (WEP) has made great progress during the past decades leading to larger and more powerful plants on- and offshore. However unexpected failure of components followed by drop out of energy production will lead to economic losses. An early detection of damage allows the operator to better plan necessary maintenance actions. Thus in parallel to the development of the WEP itself the necessity to monitor the central components of the plants has been recognized. Therefore monitoring systems are considered to play an important role to provide higher reliability of the energy production. Recently, another aspect came into the focus: older plants reach their approved lifetime of e.g. 20 years and the question arises how to prolong the lifetime and how to provide further safe operation? The first monitoring systems for WEPs were related to operational data like wind speed, pitch angle, etc. as well as to the drive train components. These were supervised by means of condition monitoring systems (CMS). The CM-methods and systems for WEP have reached industrial standards today. These are described in CMS norms and guide lines and they found a broad acceptance in the industry. The rapid growth of WEP installations over the world, especially of expensive WEPs with more than 3MW, since the year 2000 until now, brings the need of Structural Health Monitoring (SHM) of WEPs into the discussion. The idea was firstly welcomed with enthusiasm and different approaches transferred from civil and aeronautical engineering were originally adapted to monitor WEPs. The application of these approaches with the necessary measurement equipment to real WEPs during the last years have demonstrated interesting possibilities, but also their limitations and open challenges in the real field. Today the acceptance of WEP-SHM-Systems in the industry seems to be constricted, also the development of norms and guidelines on this sector progresses slowly. The reason for this current moderate acceptance is based in the higher investment on one side and the limited long-term robustness of the sensor systems and to some extent an insufficient significance of the delivered information regarding damage location and severity on the other side. Moreover uncertainties and tolerances in the manufacturing and design and the deeper understanding of possible damages and their consequences additionally contributes to a lack of target-oriented developments in the field. However, the key for the development of well accepted SHM-systems in the industrial field seems to be founded in a long-term transparent and trustful cooperation between the WEP component manufacturer, wind park operator and SHM-system designer. This keynote presentation will show a short history of WEP development and the importance of the wind energy to the green energy supply today. In the following the significance of SHM and CMS for WEPs and the influences and mechanisms on their development will be explained. The main part of the presentation will deal with the state of the art in CMS and SHM of wind energy plants in the research field and in industrial application. This will be accompanied by a depiction of some recent developments, possibilities and limitations of different kinds of approaches and systems for damage identification including also systems for identification of fatigue sources. In this context an example for a successful industrial realization of an SHM-system for rotor blade monitoring will be briefly described.