OCEANSensor draws together European companies and research organisations developing, marketing and deploying marine biogeochemical sensors. OCEANSensor aims to improve and utilise the latest sensor, platform and communication technologies for marine biogeochemical observations. The project will refine existing sensor technologies, develop new applications, and demonstrate complete technology solutions for new, in situ marine sensors and observation systems for biogeochemical parameters in coastal and oceanic waters. The outcome of OCEANSensor will be a suite of marine in situ sensors for pH, pCO2 and O2 (fluorescent optodes), nitrate (UV hyperspectral), phosphate and silicate (electrochemical), and phosphate and ammonium (lab-on-chip technology) with upgraded Technology Readiness Levels and featuring enhanced metrological performance. The project will combine the new sensor technologies with those commercially available, and develop novel observatory packages for novel remote applications in marine systems. We will develop and demonstrate a novel benthic flux quantification system to be deployed for example for carbon capture and storage CO2 leakage monitoring. In addition, we will demonstrate the sensors for water quality and biogeochemical observations on platforms including moorings, ARGO floats, surface roaming vehicles and an easily accessible cabled observatory. The project will contribute to the successful implementation of the EU Marine Strategy Framework Directive and United Nation´s Sustainable Development Goal (SDG) 14. A key goal is to open up new application fields of the technologies, and cover a larger community of end-users. OCEANSensor will strengthen the position of European industry and research organisations working with biogeochemical sensors.