Our coastal zones are subject to increasing anthropogenic pressure. Monitoring systems are required to protect them, prevent or mitigate risks and to ensure a sustainable management of their resources. PREVIMER is a partnership between Ifremer (French Research Institute for Exploitation of the Sea), SHOM (French Hydrographic Office) and several major French institutions (www.previmer.org). It provides coastal observations, analyses and 4 days forecasts for the French coasts of the English Channel, Atlantic Ocean and Mediterranean Sea: currents, water levels, waves, temperature, salinity, turbidity, nutrients and plankton concentrations. The service includes information based on in situ, satellite observations and numerical simulations. PREVIMER products and services are used by French marine environment monitoring and maritime safety agencies, for professionals (e.g. fish and shellfish farming industry), local authorities, consultants and scientists. Many applications are targeted: marine environment monitoring (Marine Strategy), alerts in case of eutrophication (bottom oxygen deficiency, excess of biomass) or harmful algal bloom (e.g. amnesic shellfish poison produced by Pseudo-Nitzschia diatoms), on-line tracking in the marine ecosystem of the nitrogen loaded by a specific river, storm surge forecast to prevent from coastal flooding risk, drift predictions and pollutant impacts, optimizing and monitoring renewable marine energy sites. PREVIMER numerical models (physics and ecosystems) resolution varies from 2.5 km for regional models up to few hundred meters for coastal models. The regional models need boundary and initial conditions. PREVIMER is thus coupled to the Copernicus/MyOcean modelling. This allows a seamless description of the ocean from the open sea down to the coastal zone.