This session focuses on the geological storage and multifunctional utilization of the deep subsurface, with particular emphasis on the safe, efficient, and sustainable use of geological formations. Topics include CO₂ and other gas storage, underground energy storage, geothermal energy, subsurface waste disposal, resource recovery, and integrated use of depleted oil and gas reservoirs, saline aquifers, salt caverns, and other geological structures. We welcome studies addressing fluid–rock interactions, multiphase flow and reactive transport, geomechanical responses, coupled thermal–hydrological–mechanical–chemical processes, storage capacity and injectivity, containment integrity, induced seismicity, leakage risks, and long-term environmental impacts. Contributions on site characterization, monitoring and verification, numerical simulation, digital twins, laboratory and field experiments, and risk-based assessment are particularly encouraged. The session also seeks interdisciplinary studies exploring the transition from single-purpose geological storage toward multifunctional and integrated subsurface systems, including synergies among carbon storage, energy storage, geothermal utilization, waste management, and resource recovery. Field demonstrations, emerging technologies, and frameworks supporting large-scale and sustainable deployment are especially welcome.