Technical aspects of wind turbine (WT) extended life are defined by the condition that further operation can only be tolerated if safe operation can be guaranteed during the extended service life period. Life extension may be considered as a natural consequence of the service conditions. The useful life extension program involves investing in preventive and corrective activities when it is necessary to keep WTs working for 30 years, so an immediate replacement of the existing components is not required. WT operators have a pressing need to extend the life of their gearboxes and bearings due to premature failures. The importance of reliability operations forces operators to make difficult predictions and decisions regarding future failure risk for warranty renewal and maintenance and operations planning. This chapter discusses some of the maintenance strategies used in renewable energy field.