This paper will consider 4 topics: (1) the definition of health-related quality of life, (2) the measurement of health-related quality of life, (3) the relationship between exercise and health-related quality of life in the general population, and (4) the relationship between exercise and health-related quality of life in patients with COPD. The paper presents data from the National Health Interview Survey, the San Diego COPD Rehabilitation Trials, and the National Emphysema Treatment Trial (NETT).