AbstractFor the purpose of supporting decision-making processes COSYNA develops highly sophisticated scientific methods to describe the state of the North Sea ecosystems. COSYNA products range from time series at various locations and regular maps of e.g. currents, waves, salinity, temperature, chlorophyll, oxygen, etc., to routine short-term forecasts (days) for these parameters. With these products COSYNA aims to reduce the gap between operational oceanography and the various users of data and forecasts of the state of the North Sea. In order to ensure products are applicable, a two-way information flow was initiated where the users themselves can provide feedback and input to COSYNA. The most relevant phases for user interaction are the release of a product idea and product implementation. Potential users include authorities, associations (nature conservation, tourism), science, and industry (e.g. renewable energy companies). During COSYNA’s early stages a survey on user requirements identified six parameters to be most useful to the greatest number of users. These are meteorological data, current, waves, bathymetry, turbidity and water temperature. High demand was revealed for forecasts and simulations (81 %), oceanographic modelling data (76%), meteorological modelling data, reconstructions of storm surges, waves, water level, and mathematical modelling of habitats. Past user interactions, such as workshops and external evaluation of the first integrated product “Pre-operational Surface Current Fields” have clearly improved COSYNA products and their usability. In order to reach the general public COSYNA publishes brochures, flyers, fact sheets and newsletters in German and English among other activities. The communication & interaction concept aims at strengthening the status of COSYNA in the various user groups and with the general public. It needs to be constantly adapted to new developments and changing framework conditions.