This textbook is intended to be used in a lecture course for college students majoring in Earth Sciences. Planetary science provides an opportunity for these students to apply a wide range of subject matter pertaining to the Earth to the study of other planets and their principal satellites. In this way, planetary science tends to unify subjects in the Earth Sciences that are traditionally taught separately. Therefore, planetary science is well-suited to be taught as a capstone course for senior undergraduates in geology departments and as an introduction to the solar system in astronomy departments. Both groups of students will benefit because planetary science bridges the gap between geology and astronomy and it prepares geologists and astronomers to participate actively in the on-going exploration of the solar system. The subject matter is presented in 24 chapters that lead the reader through the solar system starting with historical perspectives on space exploration and the development of the scientific method. The presentations concerning the planets and their satellites emphasize that their origin and subsequent evolution can be explained by applications of certain basic principles of physics, chemistry, and celestial mechanics and that the surface features of the solid bodies in the solar system can be interpreted by means of the principles of geology.