This document provides information on membranoproliferative glomerulonephritis (MPGN). It discusses the histological characteristics of MPGN including thickening of the glomerular basement membrane and increased mesangial and endocapillary cellularity. It presents a new classification system for MPGN that is based on pathogenesis, categorizing it as immune complex-mediated, complement-mediated, or other rare causes. Immune complex-mediated MPGN can result from infections, autoimmune diseases, or monoclonal gammopathies. Complement-mediated MPGN includes dense deposit disease and C3 glomerulonephritis, which are caused by dysregulation of the alternative complement pathway.