Microwave radiometry is an extremely powerful tool for atmospheric research. It is specially suited for the investigation of the dynamical and chemical processes that are important in the depletion of the ozone layer and related phenomena of the middle atmosphere. The theoretical and technical concepts of microwave remote sensing of the atmosphere are briefly reviewed. A special weight is given to the approaches as used at the Institute of Applied Physics (lAP) of the University of Bern for ground-based instruments and sensors on aircraft and on the space shuttle. Examples of results from the different instruments in the frequency range of 20 to 200 GHz illustrate the huge potential of this technique for atmospheric research.