Hydrothermal systems exert crucial influence on volcanic hazards. For example, hydrothermal alteration can reduce the strength of edifice- and dome-forming rocks, increasing the likelihood of volcano spreading and flank collapse, and high pore pressures that develop within hydrothermal systems can promote phreatic/phreatomagmatic explosions and further increase volcano instability. On the other hand, hydrothermal systems also offer the opportunity to exploit minerals of economic interest, and their heat can be harnessed to produce energy. A detailed understanding of hydrothermal systems, fluid-rock interactions in hydrothermal systems, and the resulting effects of alteration, using multidisciplinary studies, is required to better anticipate the hazards posed, to exploit the economic opportunities they provide, and to execute engineering design. We invite diverse contributions dedicated to the characterisation, imaging, monitoring, and hazard/economic assessment of volcanic hydrothermal systems and associated fluid-rock interactions. Contributions can be based on fieldwork, laboratory work, modelling, or a combination of these approaches. Because understanding hydrothermal systems requires multidisciplinary, collaborative teamwork, we welcome contributions based on any subdiscipline (e.g., geology, geophysics, geochemistry, engineering) and using any technique or method (e.g., geological mapping, magnetic, gravity, and spectroscopic methods, laboratory experiments, gas monitoring, numerical modelling). We hope to have a diverse session in terms of both speakers and audience.