The windowing technique was first introduced by Heinemann and Deimbacher((1)) in 1993. This method allows a locally restricted and time-dependent replacement of grids and parameters during simulations runs. Windows can represent any area of special interest in a reservoir. In most cases, this is the near wellbore area, for the purpose of resolving near wellbore effects. By applying the 3D (k-)PEBI gridding((2)) method, grids for arbitrary trajectories of advanced wells that resolve the near wellbore area and the wellbore itself can be generated. To handle detailed grids in full scale models of the timestep length must be drastically reduced. Therefore, these grids can only be used efficiently if the solution of the equations for the full, coarse model and the refined area is separated. This can be done based on a special kind of domain decomposition, which forms the theoretical basis of the windowing technique. Besides well modelling the windowing-technique has many other applications: keeping overall CPU time consumption in the order of magnitude of a conventional model, the windowing technique is not only a potential approach to replace the analytical Peaceman model((3)) in full field reservoir simulation, but also can be used for efficient well test simulation or dynamic flow based gridding. This paper presents the state-of-the-art of current window gridding techniques,and their solution methodologies.:Several examples to demonstrate the advantages of this tool for detailed and full field reservoir simulation are included.