EuroSITES (Integration and enhancement of key existing European deep-ocean observatories) project is integrating and enhancing the existing in situ infrastructure of 9 European open ocean observatories in key ocean regions across Europe from the North Atlantic to the Norwegian and Mediterranean Seas. This is being carried out regionally across Europe and vertically through the ocean Environmentalonment to include monitoring of the ocean interior, seafloor and sub-seafloor. Moorings with surface buoys are used as platforms for multidisciplinary sensors and samplers. The multidisciplinary ocean datasets of essential climate variables produced are available in near real-time for use by scientists, modellers and policy makers, industry and the general public. Specific science missions have been conducted to develop the sustained monitoring capabilities of key Environmentalonmental features e.g. pH and dissolved oxygen. EuroSITES focuses on scientific excellence, innovation, shared best practice, common data management, open data access and effective science communication. The EuroSITES fixed-point observatory platforms are a key contributor to the global ocean observing system, producing vital time-series data and acting as open ocean reference stations for other platforms.