Chronic obstructive pulmonary disease (COPD) is characterized by airflow obstruction with breathing-related symptoms such as chronic cough, exertional dyspnea, expectoration, and wheeze.1 These symptoms may occur in conjunction with airway hyperresponsiveness and may be partially reversible. Although COPD is a nonspecific term referring to a set of conditions that develop progressively as a result of a number of different disease processes, it most commonly refers to chronic bronchitis and emphysema and a subset of patients with asthma. These conditions can be present with or without significant physical impairment. Despite being a very common disease and the fourth leading cause of death in the United States,2 COPD often is a silent and unrecognized disease, particularly in its early phases.3 This article, the first of a 2-part series on COPD, reviews the epidemiology, clinical presentation, evaluation, and diagnosis of patients with COPD. The recently published Global Initiative for Chronic Obstructive Lung Disease (GOLD) criteria for the classification of COPD are discussed. The importance of spirometry in identifying patients in the early stages of the disease is stressed. The second article in the series will use a casebased approach to review the management of COPD.