A rotor for an electrical generator and a generator incorporating such a rotor, the rotor consisting of a central hub, a radially spaced concentric rim portion with rotor magnetic elements mounted upon it, and a plurality of elongate tension members extending generally between the hub and the rim, maintained substantially in tension so as to maintain the rim substantially in compression. The hub is rotatably driven by an axially spaced power drive means such as a wind or marine current turbine.