Abstract The Mount Edziza Volcanic Complex in north-central British Columbia includes a group of overlapping basaltic shields, salic composite volcanoes, domes and small calderas that range in age from 7.5 Ma to less than 2000 years B.P. The volcanic assemblage is chemically bimodal, comprising voluminous alkali olivine basalt and hawaiite, a salic suite of mainly peralkaline trachyte and comendite, plus a relatively small volume of intermediate rocks (trachybasalt, tristanite, mugearite, benmoreite). The complex is the product of five cycles of magmatic activity, each of which began with alkali olivine basalt and culminated with the eruption of salic magma. The regular chemical variation shown by almost 100 major- and trace-element analyses suggests a genetic lineage between the basic and salic members of each cycle. Least-squares mathematical modelling, indicates that the salic rocks (trachyte and comendite) have formed by fractionation of observed phenocryst and cumulate nodule mineral phases from a common alkali olivine basalt parent magma. Hawaiite is thought to be a cumulate rock, formed by partial fractionation and feldspar accumulation within rising columns of primary alkali olivine basalt. Fractionation leading from alkali olivine basalt through trachybasalt and trachyte to comendite is believed to have taken place where primary basalt became trapped in large crustal reservoirs. The early removal of olivine, clinopyroxene and plagioclase, leading to a trachytic residuum, and subsequent fractionation of mainly alkali feldspar, leading to the peralkaline end members, is consistent with major- and trace-element variation and with isotopic and REE data. The chemical diversity of the complex is attributed to its location over a zone of crustal extension where mantle-derived basalt, trapped in large high-level reservoirs, underwent prolonged fractionation.