The earth's atmosphere is a fluid that is capable of supporting wave motions whose amplitudes grow with height. This article reviews some of the evidence for the existence of these waves and outlines a simple theoretical approtioh for describing them. Finally, the article reviews the studies that have been made dealing with the interaction between the ionization and the atmospheric waves believed to exist at ionospheric heights—namely accoustic waves, evanescent waves and inter-nal atmospheric gravity waves.