Oceans cover more than 70% of earth and host a largely unknown marine biodiversity critical for future human beings. An improved knowledge of marine biodiversity at various scales (from genes to ecosystems) is required to facilitate building integrated scenarios and policies for a sustainable development as well as its conservation. Understanding species interactions, ecosystem functioning and dynamics, as well as biodiversity uses is presently a scientific challenge. Conservation of marine biodiversity is now a worldwide priority emphasized by several international conventions (UN, CBD..) and a key target for European policies and national strategies. This book provides a comprehensive review of the status and trends of marine biodiversity, an impact assessment of human activities and suggests a conceptual framework for relationships between biodiversity and human societies. Further research needs and priorities are identified to sustain the development of integrated scenarios and policies, considering a sustainable development as well as biodiversity conservation. The book is the product of a collective scientific expertise based upon international experts originating from social, biological and ecological sciences. .