An expanded version of a course on the physics of the Earth's interior by an internationally recognised expert in the field. It is a reference text providing condensed information on those essential physical topics needed by both the non-specialist scientist and student to follow the most recent developments in internal geophysics. It is a key to understanding papers covering theoretical geophysics where the basic formulae, definitions and theorems cannot be explained in detail due to the limited space and thus enables the reader to remain aware of the continuous progress being made in studying the Earth's interior.