There has been a long-standing controversy concerning the risk factors and pathogenetic mechanisms involved in the development of chronic airflow obstruction (CAO). This asthmatic constitution consisted of a predisposition to allergy, airways hyperresponsiveness, and possibly eosinophilia. Other investigators, however, regarded CAO as simply the late stage of chronic bronchitis. The term chronic obstructive lung disease (COLD) was developed to resolve what was largely a semantic difference. In subsequent years, the term chronic obstructive pulmonary disease (COPD) has come to be used more often than COLD to describe these patients. This article discusses the differences between these terms and defines the causes and risk factors associated with each.