A new consciousness of national security is spreading worldwide, due to the imperative necessity to guarantee the safety of citizens and the integrity of strategic infrastructures and services, counteracting against hidden, less predictable, and lethal threats stemming from regional conflicts, organized crime, and terrorism. Also, security involves not only Defence, but also several civilian institutional entities, such as police forces, magistrate, civilian protection, coast guards, etc. These new political scenarii of multi-national cooperation require state-of-art technologies and global systems of surveillance and protection. The "need to see" has recently accelerated due to the consciousness of Earth environment degradation, and of space observation as a privileged asset to monitor and preserve National Security. Governments are investing in Earth Observation to face these problems, e.g. to maintain a strict surveillance on environmental changes, whose effects are interrelated on a world-wide scale, and to establish the limits of sustainable development compatible with ecosystems' fragile needs, and to monitor national territory and crisis areas to ensure citizens' security and safety. Italy is contributing to these commitments through the development of new technologically advanced systems, and the promotion of multi-national partnerships for Defence and homeland security. Within this framework, COSMO-SkyMed is the most important Italian initiative to put into space a constellation of four satellites each carrying a Synthetic Aperture Radar (SAR) instrument for Earth Observation devoted to both Defence and civilian utilization, with superior performances, operational versatility, and imaging quality.