The tooth profile for this extended contactharmonic drive gearing Appartus is defined by the equations: X=d/8[2θ-sin (2θ)]+1⁄2{u(θ)× h(θ)};and Y=d/4[1-Cos (2θ)]; where X and Y are the curve coordinates. The invention also comprises a harmonic drive gearing apparatus for transmitting rotary motion from an input drive to an output drive, including a rigid circular spline; a flexible flexspline arranged radially adjacent the circular spline; an oval wave generator arranged radially adjacent the circular spline adapted to deform the flexspline into a corresponding oval shape when rotated, to generate a rotative motion between the flexspline and the circular spline, each of the flexspline and the circular spline having a tooth profile which accommodates tooth inclination ofup to about 2 degrees to eliminate tooth interference between enmeshed engaged flexspline and circular spline teeth on a harmonic drive apparatus.