An unpleasant sensation of difficulty in breathing is a common complaint in a variety of disease states. The psychophysical approach to the study of respiratory sensations has contributed greatly to the understanding of the mechanisms of dyspnea. Although dyspnea, in large part, is an expression of the sense of the effort of breathing, the intensity and quality of the subjective experiences during breathing are also dependent on afferent feedback primarily from receptors in the respiratory muscles. These inputs may act either by changing the level and pattern of respiratory motor activity or by a direct effect on higher brain centers. Finally, the expression of the symptoms of dyspnea in patients with cardiopulmonary disease is shaped by individual behavioral styles, personality, and emotional state. All of these factors must be taken into consideration in the management of the dyspneic patient.