A desmodromic cam driven variable valve timing (VVT) mechanism includes dual rotary opening and closing cams for actuating a rocker mechanism that drives valve actuating oscillating cams. The dual rotary cam drive positively actuates the rocker mechanism in both valve opening and valve closing directions and thus avoids the need to provide return springs as required in prior cam driven mechanisms to bias the mechanisms toward a valve closed position. A variable ratio slide and slot control lever drive as well as a back force limiting worm drive for the control shaft are combined with the desmodromic cam mechanism to provide additional system advantages.