This paper describes a hybrid optical-inertial tracking technology for fully-immersive projective displays. In order to track the operator, the operatorwears a3DOFcommercial inertial tracking system coupledwith a set of laser diodes arranged in a known con.guration. The projection of this laser constellation on the display walls are tracked visually to compute the 6DOF absolute head pose of the user. The absolute pose is combined with the inertial tracker data using an extended Kalman .lter to maintain a robust estimate of position and orientation. This paper describes the basic tracking system including the hardware and software infrastructure.