Ocean warming is reducing marine biodiversity, with changes observed all over the world. What does this mean for life on our planet, and what can we do to protect it? To protect ocean biodiversity, decisions must be based on sound science. That requires inventorying and monitoring the ocean. And because 70% of the planet s surface and 95% of the biosphere are ocean, we need all hands-on deck. UNESCO s citizen science eDNA Expeditions span 21 World Heritage marine sites around the world. This groundbreaking initiative demonstrates that people of every nation and of all ages can help document the ocean s rich biodiversity and the changes already underway. This report describes UNESCO s first global eDNA initiative, methods, and findings, including the many fascinating species identified. It includes on-the-ground stories of citizen science, inspiring readers to get involved in science and contribute to safeguarding our planet. Regular eDNA monitoring as described in this report can provide the critical information needed to actively manage and protect marine biodiversity and help reach the global target of protecting 30% of the ocean by 2030.