The oceans cover more than 70% of the Earth's surface. Nevertheless, the world's seas, especially in the deeper regions, have been less explored than the surface of the Moon. Of the 1.4 million suspected species, at most one third have been described so far. Additionally, the vast bodies of water on Earth are by no means static but are constantly in motion. Large-scale shifts caused by ocean currents, for example, are globally significant for the world's climate. The volume "World Oceans" addresses not only their importance as a source of food and raw materials or as a transportation and recreational area, but also as a space for the future and an ecosystem that is essential for our life and survival.