The aim of this book is to become THE reference text for gravitational-wave physics, covering in detail both the experimental and the theoretical aspects. It is he only existing book on gravitational waves, and it will likely remain unique for its broadeness and scope. It brings the readerto the forefront of present-day research, both theoretical and experimental, assuming no previous knowledge of gravitational-wave physics. Part I of this volume is devoted to the theory of gravitational waves. Here we have rederived - in a coherent way - most of the results that we present, clarifying or streamlining existing derivations. Part II is devoted to a description of experimental GW physics. We discuss in great detail exisiting and planned experiments, as well as data analysis techniques.