Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hematological disorder characterized by hemolysis, cytopenias, bone marrow dysfunction, and thrombosis. Over the last 20 years, we have seen a dramatic unraveling of the pathophysiology of this rare and complex disorder. As a result, new therapies involving complement inhibition have been developed, changing our understanding of the disease and improving outcomes for affected patients.