Abstract: The dynamo for/on bicycles comprises a housing (1) which can be secured to the bicycle and accommodates a stator (2) and a rotor (3); the rotor (3) can be set in rotary motion by a drive member (4), which can be driven by a bicycle wheel.The drive member (4) is mounted rotatably around a wheel axle (6) so as to be kinematically connectable with the wheel and forms part of an engageable and disengageable dynamo gearing (7) which rotates the rotor (3) in dependence on the rotation of the wheel.The dynamo is arranged with its drive member (4) coaxial to the wheel axle (6) and mounted torsionally securely on the wheel axle (6), the stator (2) and rotor (3) lying in eccentric relation to the wheel axle (6).The drive member (4) formed as a rotary housing cover has an engaging and disengaging member (22) with a driver (38) which can be pushed between the wheel spokes for transmission of the movement.