A satisfactory method for measuring the range of motion of the neck and head is needed in physical therapy, especially in view of the current number of patients with injuries of the cervical spine resulting from automobile accidents. The purpose of the present study was to develop an objective method for measuring head motion and to investigate its reliability. Although clinicians now have methods for measuring the total range of head motion in the various planes of movement, none of the objective methods measure ranges of specific motions in relation to the total range of motion from an established neutral point. This report consists of two parts. Part I deals with a review of methods of measuring joint motion, and Part II with experimental data from measurement of the head motion of thirty male subjects between the ages of twenty and forty years.