The emphasis of this book is on comparative aspects of planetary atmospheres, generally meaning comparison with the Earth, including atmospheric composition, thermal structure, cloud properties, dynamics, weather and climate, and aeronomy. The goal is to look for common processes at work under different boundary conditions in order to reach a fundamental understanding of the physics of atmospheres. As part of a general Physics course, the material is chosen to emphasise certain aspects that will be of broad topical interest: - evolutionary processes, setting the Earth in its context as a planet and a member of the Solar System - the properties of atmospheres that affect the climate near the surface of each planet - measurement techniques and models, where the same experimental and theoretical physics is applied under different conditions to investigate and explain atmospheric behaviour. These might be thought of as the astronomical, environmental, and technical sides of the discipline respectively. The book covers the basic physics of planetary atmospheres in a single text for students or anyone interested in this area of science. The approach is the same as in the author's Elementary Climate Physics: an overview, followed by more detailed discussion of key topics arranged by physical phenomenon and not planet by planet as usually found in this field. There is an emphasis on acquiring and interpreting measurements, and the basic physics of instruments and models, with key definitions and some historical background in footnotes and in the glossary at the end of the book.