There have been a number of different suggestions as to the cause of the observed ozone decline over middle latitudes. Here, the particular impact of polar processes on the middle latitude lower stratosphere is discussed. Recent studies suggest that air, recently activated and then torn from the edge of the polar vortex, contributes to the observed ozone decrease. For example, observational and modelling studies both indicate that there is an important role for filaments of vortex air being stripped away from the vortex edge. However, there appears to be little support for the idea of the vortex as a massive ‘flowing processor’ through which large quantities of air, primed for ozone destruction, are transported.