The project OceanNETs aims to determine to what extent, and under what conditions, the large-scale deployment of ocean-based negative emission technologies could contribute to achieve climate neutrality. Humanity cannot limit global warming to 1.5 °C unless much more action is taken. In addition to reducing emissions to nearly zero, humanity must also actively remove CO2 from the atmosphere. The OceanNETs project brings together the expertise needed to answer major open questions concerning ocean-based Negative Emission Technologies for climate stabilization.