Fractured-porous media and karst systems remain among the most challenging geological media to investigate due to their high heterogeneity and scale-dependent flow and transport properties. Given their abundance, they are important for various research fields such as hydrogeology, geothermal energy, CO₂ storage and nuclear waste repository management, as well as petroleum and mining engineering. Decades of research have explored a broad spectrum of methods, including field experiments, laboratory-scale approaches, analytical techniques and numerical modeling. However, the multiscale nature of these systems requires bridging micro- and macro-scale processes in order to accurately represent flow and (reactive) transport processes. In this session, we therefore welcome contributions that focus on flow and (reactive) transport in karst systems and fractured-porous media. Topics include, but are not limited to: (1) advances in field methods and laboratory techniques to characterize flow and transport from pore to field scales; (2) numerical and analytical modeling approaches for multiscale process understanding; (3) studies targeting the management and efficient use of geothermal, mineral and petroleum resources; and (4) studies targeting water resources management and environmental risk assessment.