The provision of ATM services has for a long time been a national monopoly, with the important role attributed to the nation state (by ICAO) of managing air traffic safely in its national airspace. In addition, provision of air traffic services (ATS) has traditionally been considered a natural monopoly due to the large infrastructure investments. These elements are now both changing. The European Union is increasingly entering the air traffic management world, opposing the national character of the industry and increasing the scale at which air traffic services could be provided. In addition, technological changes are more and more reducing the need for large scale ground-based infrastructure and expensive equipment, putting into question the natural monopoly character of the industry. Therefore today is the right time to study the liberalization and introduction of competition in the ATM sector. However, competition can be introduced at various levels and in different ways.