In this chapter we analyze air navigation as a whole, including an introduction and historical perspective in Section 10.1, the technical and operational framework, the so- called CNS-ATM concept, in Section 10.2, Section 10.3, and Section 10.4. Finally, in Section 10.5, we analyze the project SESAR, giving an overview of future trends in the air navigation system. A good introduction is given in Sáez and Portillo . In depth studies that can be consulted include Sáez et al. , Saéz Nieto , Pérez et al. , and Nolan .