Antineutrophil cytoplasm antibody (ANCA)–associated vasculitis (AAV) is a group of vasculitides characterized by small-to-medium-sized blood vessel vasculitis and the presence of ANCA. Although our understanding of the causes of AAV remains limited, new information supporting an autoimmune basis is emerging. This review highlights recent progresses in etiology, pathogenesis, classification, and treatment. A genome-wide association study has confirmed a role for genetic susceptibility in AAV, and links between environmental factors and AAV induction through abnormal neutrophil extracellular traps has been demonstrated. Ongoing international consensus initiatives have revised approaches to the classification of vasculitis that has been enhanced by the analysis of large-scale prospective clinical data sets. New autoantibodies to human lysosome–associated membrane protein-2 antibody, moesin, and plasminogen have been detected in AAV sera and a prognostic classification of renal biopsies developed. Clinical trial networks have extended the evidence base for the treatment of AAV, and rituximab has emerged as an alternative to cyclophosphamide for remission induction. Long-term outcomes following current treatment strategies have been determined and increased risks for cardiovascular and malignant disease reported.