Abstract: A turbine which rotates in the same directional sense for both directions of throughflow of a working medium contains rotor blades possessing an aerofoil-shaped profile which at least over a portion of the length of the rotor blades is subdivided into profile parts or portions in order to improve the flow of the working medium about the rotor blades. The profile parts of the rotor blades are non-symmetrically constructed or arranged at least in part with respect to each plane which is perpendicular to the momentary throughflow direction of the rotor. It is therefore possible to reduce the dimensions of the turbine with essentially the same power output. Such type of turbine is particularly suitable for extracting energy from the movement of waves of bodies of water, such as the sea water of the ocean, and air moved by the waves alternately in opposite directions serves as the working or flow medium.