This guide is the result of along-term process, lasting almost three years, carried out by groups of experts from different disciplines and reviewed and edited by different groups as well as by marine scientists and educators outside the groups. These MSL guide has with seven essential principles and 43 fundamental concepts, all adapted to the specificities of the Mediterranean Sea. The MSL principles and concepts, which serve as guidance to educators, teachers, scientists, non-governmental organizations, policymakers, the blue business sector, as well as the general public, are expected to raise awareness and help to create a Mediterranean-Sea-literate society.