Dynamic bidirectional exchanges between groundwater and surface water systems give rise to critical transition zones - including the hyporheic zone, the benthic layer, riparian corridors, wetlands, and lake sediments - where unique hydrological, biogeochemical, and ecological processes converge. These transition zones regulate the transport and transformation of nutrients, microplastics, and pollutants across hydrological copartments and associated aquatic ecosystems. They also control the availability of heat, oxygen, and organic matter within sediments, shaping habitat conditions for microorganisms and macroinvertebrates. Despite intese research, further investigation is needed to establish a comprehensive understanding of the physical, biogeochemical, and ecological processes occurring at groundwater-surface water interfaces, and their implications for fluvial ecology and limnology. Furthermore, it is essential to consider how exchange fluxes respond to environmental and climate factors associated with different spatial and temporal scales, spanning the sediment layer, river channel, alluvial aquifer, and regional groundwater scales. Upscaling and downscaling of a general conceptual framework, as well as enhancing process comprehension, are identified as the most significant challenges in this field of research. We invite contributions that focus on the development and application of novel experimental methods for studying physical, biogeochemical, and ecological conditions at the groundwater-surface water interfaces in rivers, lakes, riparian zones, and wetlands. One of our main interests lies in investigating the role of hyporheic processes in the retention and natural attenuation of nutrients and pollutants, and their influence on surface and groundwater quality. Additionally, we encourage research involving hydrological, biogeochemical, and ecological modeling approaches (e.g. transient storage models, coupled groundwater-surface water models, etc.). Finally, we welcome presentations that investigate the impact of groundwater-surface water interactions on management and risk assessment in view of the European Water Framework Directive.