Hydrothermal systems overlie most volcanic systems worldwide impacting the interpretation of a wide range of geophysical, chemical, and visual indicators of volcanic unrest. They also work to mask the effects of underlying magma and contribute considerable uncertainty in the interpretation of hazards and risk at volcanoes. We seek contributions from petrology, physical volcanology, geochemistry, seismology and geophysics which examine specifically the hydrothermal effects on magmatism. Of particular interest are the range of new laboratory experiments and modelling which help to constrain hydrothermal-magmatic system interactions in the shallow crust. The central aim of the session is to examine the range of observations, experimental work and models towards the goal of building a ‘toolbox’ to discriminate between mostly hydrothermal processes and mostly magmatic ones. This toolbox may then be applied in a monitoring paradigm to better understand volcano unrest and hazards