Public opinion share a deep concern on the environmental impact of pollutants emitted by transport vectors in the air. Even if ships contribute to only 3.5% of the total CO₂ emissions, all the marine stack-holders shall join in the objective of further reducing the emission levels from ships in the next few years. IMO projections say that shipping emissions may increase between 10% and 30% by 2020: to counteract this tendency without cutting cargo volume, it will be necessary to improve the energy efficiency of the ships of about 4%÷5% per year. Furthermore, we shall also have to comply with the international regulations which shall get stricter and stricter. IMO Guidance for the development of a Ship Energy Efficiency Management Plan (SEEMP) provides general recommendations to the major ship stack-holders on how to improve a the energy efficiency on board. It is recognized that monitoring of performance is the pivot around which the SEEMP is cycling as it provides a concrete basis upon which to set-up the planning and evaluate the results thus leading to the requirement for further improvement. Continuous on-line monitoring and immediate availability of all relevant data to the ship stack-holders is also the cornerstone of any progress towards increased ship autonomy. The above quoted IMO Guidance recommends that the energy efficiency of a ship should be monitored using as indicator the Energy Efficiency Operational Index (EEOI), based on total fuel consumption of the ship for each voyage. Monitoring systems developed by CETENA share the same principle, collecting signals from several heterogeneous systems and sensors of the ship, but provide a comprehensive and structured data repository in order to validate design, report and display statistical data and key performance indicator, enhance operative performance of the ship in terms of propulsion efficiency, fuel consumption and CO₂ emissions.