Rainer Helmig’s research interests are related to multi-phase physics in porous media, the development of thermodynamically consistent model concepts and their transfer to robust and efficient numerical schemes. These models are applied to environmental problems such as CO2 and energy storage in the underground; the influence of these applications on groundwater is also a focus of his research. In recent years, the modeling and analysis of soil-moisture processes in the subsurface, especially the influence of evaporation and salt precipitation in groundwater, has become a central topic of research.