<p>Subduction zone fluids are a key agent for mass transfer and energy transport at convergent plate margins. Fluid action in subduction zones is of great significance for understanding volcanism, earthquakes, crust-mantle material cycling, and the evolution of Earth’s habitability. In general, subduction zone fluids are generated by breakdown of hydrous minerals in the subducting lithosphere, and the thermodynamic stability of such minerals is dictated by the thermal structure, rock composition and tectonic evolution of subduction zones. Therefore, understanding the stability of hydrous minerals is the key to constraining the source, property, migration, and effect of subduction zone fluids. Fluid geochemistry provides an integrated approach to address this key issue. Although the existence of fluid components in subduction zones was recognized as early as the 1970s, the geochemical composition of subduction zone fluids was reasonably determined with the advances in high-pressure high-temperature experimental techniques and micro-scale <i>in-situ</i> analytical methods since entering the 21st century. The property of subduction zone fluids has been progressively recognized from aqueous solutions through hydrous melts to supercritical fluids. Current geochemical research on subduction zone fluids has integrated various major influencing factors such as the thermal structure of subduction zones, the chemical composition and physical properties of different types of fluids, and geodynamic processes of generating the fluids. This has led to a series of systematic progresses that have greatly advanced the knowledge of crustal material cycling and crust-mantle interaction in subduction zones.</p>