Based on an increasingly better pathophysiological understanding over the last 10 years, in 2010 a new classification of glomerulonephritis with dominant or codominant C3 deposits was introduced and the predominant subgoup was termed C3 glomerulopathy (C3G). In the current classification, immune complex mediated membranoproliferative glomerulonephritis (IC-MPGN) and C3 glomerulopathy (C3G) form a disease spectrum which is very heterogeneous in terms of pathophysiology and the clinical course. Recent evidence suggests that IC-MPGN and C3G share more pathophysiological aspects with respect to secondary causes, autoantibodies and genetic aspects than had been suggested with the creation of the new classification. Knowledge of the underlying pathophysiology is important for guiding the diagnostic steps for clarification of secondary causes. Comprehensive complement analysis, accompanied by antibody screening and genetic analysis, should be consistently carried out. Although not systematically validated in clinical trials, the published evidence provides a robust foundation for the use of available treatment approaches for these diseases that are often rapidly progressive and often return after renal transplantation.