In this text, integral geometry deals with Radon's problem of representing a function on a manifold in terms of its integrals over certain submanifolds--hence the term the Radon transform. Examples and far-reaching generalizations lead to fundamental problems such as: (i) injectivity, (ii) inversion formulas, (iii) support questions, (iv) applications (e.g., to tomography, partial di erential equations and group representations). For the case of the...