Thrombotic microangiopathy (TMA) is defined by clinical characteristics including microangiopathic hemolytic anemia, thrombocytopenia, and pathologic evidence of endothelial cell injury, as well as the resulting end-organ damages. Atypical hemolytic uremic syndrome (aHUS), a form of TMA, is caused by genetic or acquired defect in regulation of the alternative complement pathway. Because of the incomplete genetic penetrance of aHUS, it is crucial to assess the possibility of aHUS in all patients with TMA and many complement amplifying conditions including pregnancy, malignant hypertension, transplantation and autoimmune disease. Additionally, as various technologies for genetic sequencing advances, complement genetics has had an important role in improving comprehensive understanding of the pathogenesis of TMA, especially aHUS. The genes related to aHUS include complement factor H (CFH), CD46 of membrane cofactor protein (MCP), C3, complement factor I (CFI), complement factor B (CFB), thrombomodulin (THBD), plasminogen (PLG), and diacylglycerol kinase epsilon (DGKE). Conceivably, various mutations are expected to be newly discovered in the near future. Therapeutic strategies for aHUS are based on functional recovery of the complement system. Eculizumab (Soliris®), a monoclonal antibody that targets the terminal complement component 5 (C5) inhibitor, has shown to be effective in preventing organ damage and death by inducing hematologic remission, improving or stabilizing renal functions. Ravulizumab (Ultomiris®), another humanized monoclonal antibody that inhibits complement protein C5, has been re-engineered from eculizumab to extend its half-life, resulting in a more convenient maintenance regimen compared to eculizumab. In this session, recent studies and advanced knowledge in aHUS/TMA will be summarized and presented.