In this seminar, recent work on the development of hybrid RANS/LES and enrichment of solutions at the diffuse RANS/LES interface will be presented. Based on a temporal filtering formalism, connections between the Navier-Stokes equations and the modeling of unresolved scales can be established, in particular with regard to the transition between RANS and LES, leading to the HTLES approach. The deficit of resolved turbulent structures (modelled stress depletion) observed after the RANS-to-LES transition zone is linked to a problem of non-conservation of mechanical energy, which can only be solved by introducing an active approach based on volume forcing. This active approach makes it possible to use hybrid RANS/LES in continuous embedded LES mode, and to automate resolution refinement by identifying zones according to physical criteria, paving the way for more reliable use of hybrid RANS/LES for applications.