Wind turbines for electricity production are increasing drastically these years both in production capability and in size. Offshore wind turbines with an electricity production of 5 MW and larger are now being produced. The main failure modes are fatigue failure of wings, hub, shaft and main tower, local buckling of main tower, and failure of the foundation. This paper considers reliability-based optimal inspection and maintenance planning of wind turbines. Different formulations are considered of the objective function including benefits, building costs of the wind turbine, inspection and maintenance costs, and failure costs. Different reconstruction policies in case of failure are considered, including systematic reconstruction in case of failure, no reconstruction and failure of the control system. The concept of generic inspection and maintenance planning coupled with information from continuous monitoring is presented and illustrated. Illustrative examples for offshore wind turbines are presented, and as a part of the results optimal reliability levels for the different failure modes are obtained.