The climatology and interannual variability of wave–mean flow interaction in the Southern Hemisphere (20–80°S, 0–55 km) is described for the winter months of June–September based on a sample of four years, 1979–82. The stratospheric jet stream shifts downward and poleward over the course of the winter in response to seasonal variations in thermal forcing. The shift occurs at different times in different years, however, so that the months of July and August show substantial interannual variability of monthly mean zonal winds. The poleward and downward shift of the jet axis in an individual year is usually abrupt and occurs in association with a burst of upwardly propagating planetary waves. The driving of the mean flow in the stratosphere generally has a dipolar structure with easterly accelerations near 40°S and westerly accelerations in polar latitudes. The structure of the wave driving is consistent with the structure of the observed mean flow accelerations. Abstract The climatology and interannual variability of wave–mean flow interaction in the Southern Hemisphere (20–80°S, 0–55 km) is described for the winter months of June–September based on a sample of four years, 1979–82. The stratospheric jet stream shifts downward and poleward over the course of the winter in response to seasonal variations in thermal forcing. The shift occurs at different times in different years, however, so that the months of July and August show substantial interannual variability of monthly mean zonal winds. The poleward and downward shift of the jet axis in an individual year is usually abrupt and occurs in association with a burst of upwardly propagating planetary waves. The driving of the mean flow in the stratosphere generally has a dipolar structure with easterly accelerations near 40°S and westerly accelerations in polar latitudes. The structure of the wave driving is consistent with the structure of the observed mean flow accelerations.