This issue of Advances in Pulmonary ­Hypertension focuses on forms of pulmonary hypertension (PH) for which Food and Drug Administration–approved specific therapies are limited or nonexistent. While these diseases share some similarities in clinical presentation and hemodynamics with pulmonary arterial hypertension (PAH), there are differences in pathogenesis and, often, the coexistence of lung or left-sided heart disease which make clinical management more challenging. We are thankful to our authors and roundtable participants for their outstanding contributions to this issue. A review of these articles will demonstrate that these diseases, while similarly affecting the pulmonary vasculature, are quite different