The nature of research in the atmospheric sciences is changing rapidly in what may be thought of as three distinct revolutions, each involving a different level of the atmosphere and each in a different stage of development. The first revolution, in meteorology and climatology, has been brought about by weather satellites, giant computing facilities, and carefully coordinated international research programs; it is already well advanced. Public concern over the future of the ozone layer has spawned the second revolution, which involves the middle atmosphere (the region between about 15 and 100 km in height); this revolution has just begun. The nature of the third revolution is only now becoming apparent. It concerns the study of the atmosphere above about 100 km, a study that I shall call ionospheric physics.