As stated by the marine research decision makers in Europe in the “Ostend Declaration” in 2010, a major challenge is to support the development of a truly integrated and sustainably funded European Ocean Observing System. This will be achieved with more long-term measurements of key parameters but is impaired by the costs and lack of reliability of ocean sensors in general. The NeXOS project aims to improve the temporal and spatial coverage, resolution and quality of marine observations through the development of cost-efficient innovative and interoperable in-situ sensors deployable from multiple platforms, and Web Services for key domains and applications. This will be achieved through the development of new, low-cost, compact and integrated sensors with multiple functionalities including the measurement of key parameters useful to a number of objectives, ranging from more precise monitoring and modelling of the marine environment to an improved assessment of fisheries. Seven new compact, cost-efficient sensors will be developed, based on optical and acoustics technologies, addressing a majority of descriptors identified by the Marine Strategy Framework Directive for Good Environmental Status. Two of the new sensors will specifically contribute to the Common Fisheries Policy with variables relevant for an Ecosystem Approach to Fisheries. All new sensors will respond to multiplatform integration, sensor and data interoperability, quality assurance and reliability requirements. These will be specified for each new sensor system. All new sensors will be calibrated, integrated on several types of platforms, scientifically validated and demonstrated. One of the main objectives of NeXOS will finally be to enhance the competitiveness of European SMEs in the ocean sensor market. To this end, sensor requirements and specifications will be assessed at an early phase of the project for market penetration.