One of the most challenging problems in electrical engineering is the detection and localization of target in underwater acoustics. In particular, bearing estimation is usually obtained by the classical array processing method, beamforming. High-resolution methods have been introduced to overcome the main limitation of beamforming, poor resolution. This volume is composed of tutorials and state-of-the-art research papers on high-resolution methods applied to underwater acoustics. Most of these papers are related to the bearing estimation problem (detailed presentation of methods of their performances, both theoretical and at-sea, their use with an array of unknown geometry, etc) but extensions to the temporal and spectral domains are also included. This monograph on signal processing, underwater acoustics is intended for the use of electrical engineers, advanced students, researchers, industry engineers and scientists, technical navy people.