Chylothorax, the accumulation of chyle in the pleural space, is a relatively rare cause of pleural effusion in children. It can cause significant respiratory morbidity, as well as lead to malnutrition and immunodeficiency. Thus, a chylothorax requires timely diagnosis and treatment. This review will first discuss the anatomy and physiology of the lymphatic system and discuss various causes that can lead to development of a chylothorax in infants and children. Then, methods of diagnosis and treatment will be reviewed. Finally, complications of chylothorax will be reviewed. Pediatrics 2014;133:722-733