Quality of life measurement within the medical context takes a very different approach from that adopted by the social sciences. Within medicine, the construct is referred to as health-related quality of life (HRQOL) which relies heavily on measuring symptoms of ill-health. Within the social sciences, quality of life is conceptualized as a global construct, positive in nature, encompassing, but not limited by health. This chapter contrasts these two views. It is evident that these are serious issues concerning measurement of HRQOL, to the extent that the instruments may not be regarded as valid measures of quality of life as the term is generally understood. The global measures of subjective well-being, while valid and theoretically embedded, are also limited by their relative insensitivity to medical health. The reason for this insensitivity is proposed to be a homeostatic system that normally maintains subjective quality of life within a narrow positive range.