This unique book presents an overview of isostasy, a simple concept of fundamental importance to the Earth Sciences that students have traditionally found difficult to grasp. With this in mind, the author has used a simplified mathematical treatment, numerous geological examples and an extensive bibliography, to make the subject more accessible and easy-to-understand. Beginning by tracing the ideas behind local and regional models of isostasy and arguing that only flexure is in accord with geological observations, the book proceeds to describe the theoretical background, the observational evidence and the constraints that flexure has provided on physical properties of the lithosphere. The book concludes with a discussion of flexure's role in understanding the evolution of the surface features of the Earth and its neighboring planets. Ideal for graduate students of geophysics, geodesy and geoscience, it will also be of interest to researchers in gravity and geodesy, tectonics and basin analysis.