Planetary aeronomy as a study of the interaction between the stellar radiation and particle environment with planetary upper atmospheres now finds its application more and more in time newly detected exoplanets. Terrestrial exoplanets may also exist around other stars such as the many giant Jupiter-class exoplanets already discovered within the solar neighborhood. Space-borne telescopes will detect these planets in the near future and will characterize their atmospheres by interferomnetric and/or coronagraphic imaging. The discovery of other Earth-size planets in various orbital distances to their host stars will also enhance our understanding of the evolution of the terrestrial atmosphere in contrast to the CO2 atmospheres of Venus and Mars or reduced secondary atmospheres of icy bodies like Saturn’s large satellite Titan. Studies related to planetary aeronomy will therefore contribute to investigations of evolutionary processes, the stability of planetary atmospheres and their water inventories and the characterization of exoplanetary atmospheres as well as in a more detailed classification of the Habitable Zone (HZ).