Eleven planetary atmospheres are included for detailed study in this reference/text, four for the giant planets (Jupiter, Saturn, Uranus, and Neptune), four for the small bodies (Io, Titan, Triton, and Pluto), and three for the terrestrial planets (Mars, Venus, and Earth). The authors have carried out a comprehensive survey of the principal chemical cycles that control the present composition and past history of planetary atmospheres, using the database provided by recent spacecraft missions supplemented by Earth-based observations.