Chronic obstructive pulmonary disease (COPD) and asthma are the main causes of obstructive lung disease, and mortality rates of both diseases are on the increase. Smoking is the major risk factor for COPD. Airway hyperreactivity and reversibility of airflow obstruction, once considered hallmarks of asthma, may also be seen in COPD. Asthma is increasingly being recognized as a chronic inflammatory airway disease. COPD and asthma can be diagnosed through careful history taking, physical examination, spirometry, and other ancillary tests. More widespread use of peak expiratory flow rates should aid in diagnosis and monitoring.