This book on Marine Radioactivity sets out to cover most of the aspects of marine radioactivity which have been the focus of scientific study in recent decades. The authors and their reviews divide into topic areas which have defined the field over its history. They cover the suite of natural radioisotopes which have been present in the oceans since their formation and quantitatively dominate the inventory of radioactivity in the oceans. Also addressed are the suite of artificial radionuclides introduced to the oceans as a consequence of the use of the atom for development of nuclear energy, nuclear weapons and various applications of nuclear science. The major source of these continues to derive from the global fallout of atmospheric tests of nuclear weapons in the 1950s and 1960s but also includes both planned and accidental releases of radioactivity from both civilian and military nuclear technology. The other division of the major study direction depends on whether the objective is to use the radionuclides as powerful tools to study oceanic processes, to describe and understand the ocean distribution of the various natural or artificial radionuclides or to assess the different radionuclides' impact on and pathways to man or marine organisms.