Pulmonary surfactant research is considered from the perspective of interdisciplinary correlations based on information acquired from biophysics and physical chemistry, biochemistry, cell biology, physiology, and medicine. Current views of the important molecular constituents of the pulmonary surfactant system are described and related to the biophysical surface properties necessary to generate appropriate effects on respiratory physiology. The fundamental importance of multidisciplinary characterizations of lung surfactant, together with correlations between these descriptions, is stressed throughout. The primary advantage of such an approach is that it provides broad but coordinated principles and data with which to test hypotheses of lung surfactant function and roles in respiratory physiology and pathophysiology. This perspective is used to examine available information about the functional composition of lung surfactant, its surface tension-lowering properties at physiological temperature and humidity, and considerations relevant to the formulation of effective exogenous surface-active mixtures in the treatment of surfactant-deficient states. Also discussed is the biophysical state in vivo of pulmonary surfactant at the alveolar level, including current knowledge of the alveolar hypophase as well as the concept of functional surfactant acting in predominantly dry alveoli in the normal lung.