Abstract: Atmospheric waves provide an effective mechanism for exchanging energy, momentum and chemical constituents between different atmospheric regions. This talk is devoted to the study of gravity waves in the atmospheres of Solar System planets using various theoretical and observational approaches in the framework of comparative planetology. I will focus on the results of a number of ground based observations and ongoing experiments from current NASA space missions to Jupiter, Saturn and Mars. These observations aim to constrain the spectral characteristics of the present gravity wave modes and to understand the dominant sources of wave activity in the atmospheres of giant and terrestrial type planets. I will also present preliminary results on the presence of ammonia clouds in Jupiter's atmosphere based on an analysis of the data from the Cassini spacecraft en route to Saturn.