Exploration of the oceans using geophysical methods has had a profound effect on the way we view the structure of the Earth and its behaviour through geological time. Geophysics has also played a vital role in the search for petroleum and other natural resources lying beneath the seabed. This volume on marine geophysics has two objectives: to provide a comprehensive review of techniques and to examine what geophysical observations can tell us about the structure and tectonics of the oceans. Central to geophysical work at sea are the means of locating observations accurately and determining in detail the morphology of the sea floor. These topics are discussed early in the book. Considered next are the powerful seismic techniques for imaging the Earth's interior from shallow coastal areas to the deep-sea trenches. Further chapters; focus on the gravity and magnetic fields over the oceans, heat flow, electrical and radiometric methods and measurements in offshore boreholes. In later parts of the book, wide-ranging geophysical observations are brought together in chapters on the development of the modern oceans, the structure of their deep basins and the nature of their aseismic and seismically active margins. This book will be of interest to marine scientists and advanced undergraduates and postgraduates following courses on, or undertaking research in, geophysics, marine geology, oceanography, physical sciences, remote sensing, marine surveying and offshore engineering.