One of the initial goals of measuring U-series disequilibria in young volcanic rocks was the development of new dating methods in an age range (about 0–300 ka), where few other methods were applicable at that time (Cerrai et al. 1965; Cherdyntsev et al. 1967; Kigoshi 1967; Taddeucci et al. 1967; Allegre 1968). In the following years, several studies showed that the 238U-230Th method, the first to be applied, was indeed able to give reliable ages on rocks from various volcanoes (e.g., Allegre and Condomines 1976; Condomines et al. 1978). But it was soon realized (e.g., Oversby and Gast 1968; Allegre and Condomines 1976; Capaldi et al. 1976) that U-series disequilibria could not only be used to date volcanic rocks, but also to infer the timescales of magma transfer and evolution in the crust, and that these methods could give rather unique information on such important parameters. During the last twenty years, besides continuing efforts to develop and discuss the U-series dating methods, many studies have addressed the problem of the timescales of magmatic processes, from melting in the mantle, to crystallization and differentiation of the magmas in their reservoir(s), and magma degassing near the surface. Moreover, as far as studies on volcanic minerals are concerned, determining the eruption age and the timescales of crystallization are intimately linked. It is the purpose of this chapter to review some of the recent advances in the fields of magma chamber processes and dating (the timescales of partial melting in the mantle are treated in other chapters of this book: Lundstrom 2003; Bourdon et al. 2003; Turner et al. 2003). General reviews of U-series disequilibria in volcanic rocks have been published by Condomines et al. (1988), Gill et al. (1992), …