Pulmonary hypertension (PH) is a rare disease in newborns, infants, and children that is associated with significant morbidity and mortality. In the majority of pediatric patients, PH is idiopathic or associated with congenital heart disease and rarely is associated with other conditions such as connective tissue or thromboembolic disease. Incidence data from the Netherlands has revealed an annual incidence and point prevalence of 0.7 and 4.4 for idiopathic pulmonary arterial hypertension and 2.2 and 15.6 for pulmonary arterial hypertension, respectively, associated with congenital heart disease (CHD) cases per million children. The updated Nice classification for PH has been enhanced to include a greater depth of CHD and emphasizes persistent PH of the newborn and developmental lung diseases, such as bronchopulmonary dysplasia and congenital diaphragmatic hernia. The management of pediatric PH remains challenging because treatment decisions continue to depend largely on results from evidence based adult studies and the clinical experience of pediatric experts. (J Am Coll Cardiol 2013;62:D117-26) ©2013 by the American College of Cardiology Foundation.