The Vilhelm Bjerknes Medal is awarded to Karin Labitzke in recognition of her fundamental achievements in the observational study of the stratosphere and mesosphere. She has made many important contributions to increasing our understanding of these regions of the atmosphere and has led the way in discovering the influence of the 11-year solar cycle on the Northern Hemisphere stratospheric polar vortex as modulated by the Quasi-Biennial Oscillation.