Originally, beamforming meant forming the transmit beam for some purpose. Today, we use the word beamforming both for the transmit – and the receive beam. The beam is simply the mainlobe of the array’s radiation – or response pattern. Changing this pattern, either by weighting the array elements or by steering its direction, is what beamforming is all about.In most signal processing applications, there is a tradeoff between different needs.The tradeoff in bathymetric sonars is between cross-track coverage, accuracy and resolution. The goal of this thesis, is to improve the resolution of a bathymetric sonar, working only with the output of the array – after the tradeoff is done.To achieve this, the Fourier transform method for beamforming and some high-resolution, also called adaptive, methods have been studied.In this thesis, the performance of several high-resolution beamformers are studied: Minimum-Variance, Eigen-Vector, MUSIC, Minimum-Norm, root-MUSIC and ESPRIT. The conventional Fourier transform, used for beamforming in many array systems today, suffers from low resolution. It has low ability of resolving closelyspaced sources. For bathymetric sonars, this may lead to incorrect mapping of the sea-floor.Different ways of estimating the spatial covariance matrix are investigated, and a method aimed to reduce structured noise in this matrix is developed. Some quantitative measures are developed and used as part of the evaluation of the high-resolution beamformers. The measures show that estimation of the spatial covariance matrix has a large impact on the performance of the beamformers, and thatmost methods perform better when the structured noise in this matrix is reduced. An alternative approach for a high-resolution beamformer (root-MUSIC) is also developed, and is found to perform better than the one given in literature.It is found that among the high-resolution beamformers studied here, MUSIC and ESPRIT perform best with regard to the quantitative measures used for evaluation. These results are supported by visual examination of different spectra for the beamformers. Finally, some interesting research areas based on the observations in the thesis areproposed, and a new way of obtaining bathymetric measures is suggested.