Vadose zone is the unsaturated soil layer between the earth surface and the ground water table. It plays an important role within the Earth Critical Zone as a medium of transport, storage of the solutes and transfer of microorganisms to the groundwater. Within the vadose zone, water content and the solute concentration continuously fluctuate as a consequence of a number of processes, such as infiltration, leakage, evaporation, root water uptake and water redistribution. Hillslope and karstic recharge may be driven by infiltration process during major storm events, particularly in semi--arid regions while, in colder regions, snow melt may be the dominant factor. In heavily populated areas, human activities lead to several additional sources of groundwater recharge, such as irrigation and leaking urban water infrastructure, simultaneously it reduces the effectiveness of the soil water percolation. Climate warming can also reduce the groundwater recharge as a consequence of reduced snowfall, increased evaporation and increased water demand for transpiration. On the other hand, both excess of recharge with the consequent water table rise, and climate warming can lead to an increase of evaporation from the water table causing soil salinity, with crucial fallout on the soil quality. Solute and particle materials inflow to the groundwater are coupled to these processes whereas their sources are natural or from agricultural and industrial land use. Due to the complexity of the environment, the variability, and heterogeneity of the soil and non--linearity of the processes, of both anthropic and natural origin, the assessment of the water and solutes balance in the vadose zone and of the water and solutes transport between the vadose zone and the groundwater is still a major challenge. Catchment and soil hydrologists, groundwater modellers and soil scientists try to quantify such complicated non--linear processes, which remains inherently a multi--disciplinary field where experts with different background need to work together. The purpose of this session is to bring these different groups together and to discuss recent advances in the spatial and temporal monitoring and modelling approaches with respect to quantifying water and solute transport between the unsaturated zone and the groundwater.