This article reports a calibration procedure that enables researchers to track movements of the eye while allowing relatively unrestricted head and/or body movement. The eye—head calibration algorithm calculates fixation point based on eye-position data acquired by a head-mounted eyetracker and corresponding head-position data acquired by a 3-D motion-tracking system. In a single experiment, we show that this procedure provides robust eye-position estimates while allowing free head movement. Although several companies offer ready-made systems for this purpose, there is no literature available that makes it possible for researchers to explore the details of the calibration procedures used by these systems. By making such details available, we hope to facilitate the development of cost-effective, nonproprietary eyetracking solutions.