Research in Gravitational Wave Physics is presented in a unitary form. Gravitational wave emission and detection, as predicted by General Relativity, is described. Then the various sources and their characteristics are described, in view of gravitational wave detection. Signal processing methods to extract the maximum information out of noisy data are shown; after a description of current detectors, the most recent results are discussed. In the last part detectors are studied in greater detail with the areas where research and development is most active.