The phenomenal advances in sequencing technologies over the last two decades are opening up unprecedented possibilities for understanding, protecting and making the most of all forms of life in all their diversity. Organisms are linked by their DNA, inherited from common ancestors since the origin of life. This genome contains, for each organism, all the instructions necessary for the development of the embryo and the functioning of the adult. It is this colossal mine of information that the ATLASea programme proposes to decipher and exploit, focusing on the French Exclusive Economic Zone (EEZ) in mainland France and four overseas territories.