This book investigates the anomalous magnetic field of the ocean and its connection with geological structure, tectonic evolution of the oceanic lithosphere, and magnetic properties of different rock types in the oceanic crust. The book describes new instruments and techniques of gradient magnetic measurements with three sensors, as well as the new technique of processing and interpretating hydromagnetic data on the basis of adoptive filtration and reparametrization. The text provides unique data of geomagnetic surveys carried out by Russian research vessels in different regions of the World Ocean, including submersible apparatus and ingenious theoretical and experimental technology of the magnetic modeling and investigations of the nature of magnetic anomalies. The results of systems analysis of geochemical content and composition during the mid-oceanic ridge basalt are presented.