A steerable drilling system includes a drill string carrying a bent housing, the bent housing containing or having associated therewith a drive motor arranged to drive a drive shaft angled to an axis of part of the drill string adjacent the bent housing, and an orientating motor permitting relative rotation between the drill string and the bent housing, the orientating motor driving the output shaft in a reverse direction relative to a direction of rotation of the drill string to form a curve in a borehole being formed.