This chapter traces the development of the epidemiology of chronic respiratory disease. The modern era of the study of the epidemiology of chronic obstructive pulmonary disease (COPD) did not blossom until the middle of the 20th century. Before that time clinicians generally believed that much of the symptomatology associated with the disease represented a ‘normal’ state. In the last fifteen years, much of the epidemiological research has been directed to identifying the characteristics of these subgroups at risk before clinical disease is apparent.