Mathematical physics is concerned with mathematical modeling of physical phenomena. Most often this leads to a mathematical model in terms of (partial) differential equations. In fact, differential equations present the main theme in our group and we employ both analytical and numerical solution methods. Simulation using computer implementations of models with a practical significance have a large impact on our research. A close collaboration exists with external partners, such as Shell, TNO, Deltares. A rather unique feature of our group is that we often consider large scale systems in relation with large scale computer models and that we address the specific mathematical questions arising from this. We mention data assimilation (coupling of model and measurements), flexible numerical methods (numerics for real-life applications), high-performance computing (enlargement of scale), multiple scale analysis and asymptotics (model simplification), and stochastic differential equations (dealing with uncertainties).