Radioactivity in the marine environment, although present since the Earth’s formation, is comparatively understudied in contrast to aerial and terrestrial environments. A thorough examination of the radioactivity levels in aquatic environments can establish a robust foundation for comprehending various geochemical processes and phenomena within the water column and near the seabed, and as a result estimate the impact of radioactivity on local ecosystems. To achieve this objective, in-situ, long-term, and continuous monitoring is required. The present part I of the white paper highlights the fundamentals of marine radioactivity, describes the main objectives of an ambitious EU-funded project (RAMONES: Radioactivity Monitoring in Ocean Ecosystems) and introduces the innovative aspects of the technology developed as novel solutions to open problems.