There are seven major, late Quaternary (≤1 m.y.), trachytic caldera volcanoes in the Kenya Rift Valley; the Barrier, Emuruangolgolak, Silali, Paka, Menengai, Longonot, and Suswa. These are situated in the inner troughs of the rift. Their positions are not apparently related to transverse lineaments or basement structures. The structural development was complex, involving combinations of the formation of large calderas and small calderas/pit craters, the growth of lava and tuff cones and the eruption of fissure basalts. Two groups of volcanoes are broadly distinguished. A southern group, comprising Suswa, Longonot, and Menengai, are overwhelmingly of trachytic composition. Krakatau-style formation of calderas approaching 100 km2 in area was accompanied by the eruption of voluminous ash flow and airfall tuffs (20-50 km3). In the remaining, more northerly volcanoes, basalts and mugearities form bimodel associations with trachytes. Caldera formation was accompanied by only sparse pyroclastic activity and the collapse may have been initiated by withdrawal of magma from depth. Knowledge of the geochemical evolution of the complexes is limited by the scarcity of published analytical data. The only detailed study is that of Menengai, where chemical variations were caused, at different structural stages, by magma mixing, crystal fractionation and various liquid-state differentiation processes.