Abstract: The present invention comprises an extended tooth contact harmonic drive gearing apparatus for transmitting rotary motion from an input drive to an output drive through mating contact between a flexspline and a rigid circular spline, the flexspline being swept into a non-circular shape by a wave generator. The wave generator causes the teeth of the flexspline to precess from a normal to an inclined orientation and back to a normal orientation again. The teeth on both the flexspline and the circular spline have a profile which accomodates that tooth inclination, and thus avoids interference therebetween.