We discuss the recent use of large-eddy simulations (LES) for the analysis of the flow over dunes. In large-eddy simulations the governing equations of fluid motion are solved on a grid sufficiently fine to resolve the largest eddies, while the effect of the smallest ones is modelled. Two-dimensional and three-dimensional dunes in rivers, as well as Barchan dunes in deserts are considered. Examples are shown to demonstrate how LES can be used to complement experiments, by exploiting its ability to calculate full-field information, and to highlight the temporal development of the flow. The main challenges slowing a more widespread application of this method are discussed.