MuPhi---Simulation of Flow and Transport in Porous Media. Simulation of subsurface water flow and solute transport are crucial for the prediction and control of groundwater production, the assessment of water contamination and becomes more and more important for flood and climate prediction. The highly scalable simulation program μφ for the solution of Richards’ equation is capable to describe saturated and unsaturated subsurface flow. A cell-centred Finite-Volume scheme is used for the spatial discretisation, an implicit Euler scheme for the time discretisation and an incomplete Newton-scheme for the linearisation of the non-linear equations. The linear equation system is solved with the iterative solver template library (ISTL) developed by our group in the framework of the DUNE-Project. A BiCGstab solver with an algebraic multigrid preconditioner allows the efficient and scalable solution of huge systems on massively parallel computers. In the transient solute transport part of μφ the Convection-Dispersion-Equation is solved on the flux fields generated by the water transport part using an explicit second-order Godunow discretisation with a minmod slope-limiter. Both programs require massive data I/O (for the input parameter fields and the storage of solutions and flux fields. The usage of SIONlib allows for very efficient output on parallel file systems.