Development and application of decision support systems to aquifers and underground reservoirs requires reliable and physically based methods to infer key parameters controlling multiphase flow and contaminant fluxes of conservative or reactive substances in the subsurface. Underground environments are complex and extremely heterogeneous exhibiting variations on a multiplicity of scales. Addressing heterogeneity in all its manifestations is the focus of exciting and intense forefront research and industrial activities. This general session invites presentations on recent developments in understanding, measuring, and modelling subsurface flow and solute transport processes in both the saturated and unsaturated zones, as well as across boundaries. This session is aimed at providing an opportunity for specialists to exchange information and to introduce various existing and novel alternative deterministic and stochastic models of subsurface flow and transport to the general hydrological community, with critical and timely applications to environmental and industrially relevant settings. Focus is placed on recent key developments in new experimental protocols, novel theoretical aspects and associated computational tools, fate of new contaminants, and field/laboratory applications dealing with accurate and efficient prediction and quantification of uncertainty for flow, conservative and reactive transport processes in the subsurface, in the presence of multiple information at different scales, ranging from the pore level to the intermediate and basin scales.