Pulmonary surfactant is a chemically heterogeneous material that provides a stable, low surface tension within the lung, thereby preventing alveolar collapse at low transpulmonary pressures. Both the lipid and the protein components of surfactant are important for establishing and maintaining a low surface tension. The composition of surfactant, the biogenesis of surfactant components, and the biologic roles of surfactant components are discussed in this brief review. Surfactant functions in adult lung disease and surfactant replacement therapy are also briefly considered.