Chronic lung disease is a major health problem among children. Estimates suggest that one child in six has a chronic respiratory condition. This article reviews three common chronic respiratory conditions occurring in childhood for which physical therapy is usually recommended. The cause, pathophysiology, and medical treatment are explained for asthma, respiratory complications of chronic neuromuscular disease, and cystic fibrosis. The rationale for physical therapy and the concepts of treatment for the three disorders are presented. Major clinical studies that have attempted to document the efficacy of physical therapy are discussed. Questions for future research are proposed. .