A brief introduction to a new advance in the NWP field: unified global NWP models with variable resolution is given. The principal purpose is to decrease the calculation cost of the NWP by unifying the limited area NWP model and the global spectral NWP model as an only operational one. A horizontal resolution, and a semi-implicit and semi-Lagrangian integration scheme were used in this unified NWP model. The French unified model went into operation in 1992. The results were very encouraging !