The ocean covers 70% of the surface of our planet, it plays a major role in regulating the Earth’s climate and is home to a multitude of species, many of which we have yet to discover. The ocean is crucial for the functioning of life on Earth. With global change, many issues have emerged, and the consequences of these in the future concern us all. This book improves our understanding of what the ocean is, in all its breadth, depth and complexity, from both the biological and physical perspectives, including interactions and dynamics. Many innovative tools, infrastructures and approaches are developed to explore the ocean, and to obtain the data and information that are essential to expanding our knowledge. History tells us much about the evolution of the techniques and representations connecting human communities to the oceans, and the diverse ways in which we use them. Whether we approach it in terms of its resources, its services or its territorial stakes, the ocean is not only essential, but also vulnerable. To manage the many risks associated with our seas, from submersion to pollution, we need to plan ahead in the face of increasing human activities. The ocean is often thought of as infinite and unlimited. It is seen by some as a common good, by others as a key element of geostrategic issues. This book raises the question of its future.