Exactly 100 years ago the great Canadian-born petrologist N. L. Bowen published two seminal works on the chemical differentiation of magmas in which he posed the basis for a physicochemical understanding of the fractionation of crystals from melts in molten rock. A subsequent century of research and technological advances has enhanced our understanding of the physics and chemistry of magmatic systems and their temporal evolution. The image of sub-volcanic magmatic systems has evolved greatly in that time, from a simple ‘boiling vat' concept of molten rock in which bubbles, crystals and melt separate gravitationally to a recognition that magma vats are relatively rare and that most magmatic systems spend much of their lifetime in a partially molten, or mushy, state. Real magmatic systems appear to be organized into a series of storage regions periodically connected by feeding structures transferring magma (and heat) at different fluxes. Magma fluxes between the different portions of this plumbing system, and the variation of the chemical and physical properties of magma as it rises through the crust, exert essential controls on the eruptive modalities of volcanoes and the geochemistry of their products. This book presents a collection of contributions that use petrology, geochemistry, geochronology and numerical modelling to identify the processes operating at different depths within magmatic systems and to characterize the fluxes of magma between them.