The investigations carried out within the French-German DFG-CNRS Research Initiative on 'LES of Complex Flows (FOR 507)' aimed at the development and application of hybrid LES-RANS methods for turbulent flows with separation. The objectives were twofold.On the one hand, the performance of a well-established hybrid approach, namely the detached-eddy simulation, was studied based on really challenging test cases such as the flow over the 3D hill and around the Willy car model. On the other hand, a new hybrid LES-RANS methodologywas set up which aims at overcoming certain drawbacks associated with DES. It relies on the coupling of a near-wall RANS model with LES for the outer flow which allows an appropriate representation of large-scale flow phenomena. In order to take the anisotropies in the near-wall region rigorously into account, an explicit algebraic Reynolds stress model was chosen and its performance in comparison with linear eddy-viscosity models was analyzed for different test cases such as the flow over 2D hills and in a 3D diffuser. A further advantage of the new hybrid method is that no interface predefinition is required. Instead the interface is dynamically determined on-the-fly based on instantaneous physical quantities which guarantees that local changes in the flow are accounted for. © 2009 Springer-Verlag Berlin Heidelberg.