An electromechanical rear derailleur is provided for a bicycle, including a base member for attachment to the bicycle along a mounting axis. A movable member has a cage assembly attached thereto. A linkage is provided including pivot axes oriented substantially perpendicular to the mounting axis, the linkage coupling the movable member to the base member and operative to enable movement of the movable member relative to the base member in a direction substantially parallel to the mounting axis. A power source powers an electric motor connected thereto and a transmission is coupled to and actuated by the motor to move the movable member.