Method and apparatus for installing, maintaining and decommissioning wind turbines, both onshore and offshore, comprises a crane having extendable legs that allow it to climb a tower that it is erecting in sections by engaging the tower by friction or mechanical interference. The crane may carry the wind turbine nacelle on its upper members during construction of the tower and may be fitted with a crane for handling tower sections, or it may carry an “A” crane for lifting the nacelle and its components once the tower is complete or for constructing heavy maintenance. The crane may be fitted with various lifting and handling means to facilitate maintenance or the installation, maintenance or removal or airfoil rotor blades.