THYRSIS is a new opensource QGIS extension dedicated to hydrogeological modelling of flow and transport at multiple scales, from local to regional. Based on SpatiaLite databases and time-dependent mesh layers, it is fully integrated into QGIS and allows the building of hydrogeological models. The modelling is based on 1D unsaturated vertical columns, coupled with a 2D horizontal groundwater model. Groundwater flow models can be imported or directly created with THYRSIS using the OpenFOAM cfMesh or GMSH mesh builders. Simulations are performed with the OpenFOAM porousMultiphaseFoam solvers, and the results are displayed in QGIS through the mesh layers. THYRSIS can handle several types of water or solute input in multiple zones, which can be defined at the surface or underground. Water or solute input can also be defined over the whole study area and directly in the groundwater body, ignoring the unsaturated zone. THYRSIS can therefore simulate the effect of heterogeneous, transient infiltration and reproduce variations in piezometric levels, or the transport of matter in the subsurface, from the ground to groundwater outlets, in order to estimate groundwater concentrations. Numerous functionalities are proposed such as uncertainty management, as well as the calculation and display of isolines and mass balance, time-potential or time-concentration graphs.