Magmatic crystals in volcanic rocks are one of the prime sources of information on pre-eruptive processes, and hence for our understanding of eruption trigger mechanisms and magma evolution. Recent advances in the study of single crystals provide us with powerful means to decipher the often complex interplay of sub-volcanic processes by employing methodologies such as thermodynamic modeling, experimental petrology and micro-analytical approaches that allow us to reconstruct the physico-chemical conditions within magmatic systems. This session aims to bring together researchers who investigate magmatic crystals through in-situ analyses of major, trace and volatile components, isotopes, and through experiments and numerical modeling to unravel pre- and syn-eruptive magmatic processes, magma chamber conditions, and the evolution of volcanic systems as a whole.