Chronic obstructive pulmonary disease (COPD) is characterized by poorly reversible airflow limitation. The pathological hallmarks of COPD are inflammation of the peripheral airways and destruction of lung parenchyma or emphysema. The functional consequences of these abnormalities are expiratory airflow limitation and dynamic hyperinflation, which then increase the elastic load of the respiratory system and decrease the performance of the respiratory muscles. These pathophysiologic features contribute significantly to the development of dyspnea, exercise intolerance and ventilatory failure. Several treatments may palliate flow limitation, including interventions that modify the respiratory pattern (deeper, slower) such as pursed lip breathing, exercise training, oxygen, and some drugs. Other therapies are aimed at its amelioration, such as bronchodilators, lung volume reduction surgery or breathing mixtures of helium and oxygen. Finally some interventions, such as inspiratory pressure support, alleviate the threshold load associated to flow limitation. The degree of flow limitation can be assessed by certain spirometry indexes, such as vital capacity and inspiratory capacity, or by other more complexes indexes such as residual volume/total lung capacity or functional residual capacity/total lung capacity. Two of the best methods to measure flow limitation are to superimpose a flow-volume loop of a tidal breath within a maximum flow-volume curve, or to use negative expiratory pressure technique. Likely this method is more accurate and can be used during spontaneous breathing. A definitive definition of dynamic hyperinflation is lacking in the literature, but serial measurements of inspiratory capacity during exercise will document the trend of end-expiratory lung volume and allow establishing relationships with other measurements such as dyspnea, respiratory pattern, exercise tolerance, and gas exchange.