The authors describe the Russian Stratospheric Aircraft M-55 Geophysica, an important new platform for earth observation, and describe some technical details of its inaugural mission. The M-55 has successfully conducted scientific test flights in Pratica di Mare, Rome, in November 1996, and the first Airborne Polar Experiment (APE 1) from 19 December 1996 to 16 January 1997 from Rovaniemi in northern Finland. Three test flights were carried out at Pratica di Mare, and seven scientific mission flights during APE 1, when “quasi-Lagrangian” flight paths (flights in the wind direction, assuming the stratosphere to be stationary over the flight period) and lee wave flight paths were employed. Combined sorties of the M-55 Geophysica and the DLR Falcon were performed, the latter acting as a pathfinder for the former, guiding it to small regions of intense polar stratospheric cloud activity. These small cloud patches are associated with intense atmospheric wave activity over the Scandinavian mountains and other mountain ranges, and have been implicated in the observed depletion of stratospheric ozone. The Geophysica is well suited to probing atmospheric physics and chemistry in the harsh environment of these clouds.