This is the second edition of a well-received book that is a modern, self-contained introduction to the theory of gravitational interactions. The new edition includes more details on gravitational waves of cosmological origin, the so-called brane world scenario, and gravitational time-delay effects.The first part of the book follows the traditional presentation ofgeneral relativity as a geometric theory of the macroscopic gravitationalfield, while the second, more advanced part discusses the deep analogies (anddifferences) between a geometric theory of gravity and the gauge theories ofthe other fundamental interactions. This fills a gap within the traditionalapproach to general relativity which usually leaves students puzzled about therole of gravity. The required notions of differential geometry are reduced tothe minimum, allowing room for aspects of gravitational physics of currentphenomenological and theoretical interest, such as the properties ofgravitational waves, the gravitational interactions of spinors, and thesupersymmetric and higher-dimensional generalization of the Einstein equations. This textbook is primarily intended for students pursuing a theoretical or astroparticle curriculum but is also relevant for PhD  students and young researchers.