The Federal Aviation Administration's (FAA) Air Traffic Organization (ATO) provides air traffic control (ATC) services within U.S. and certain international airspace. U.S. airspace is the most expansive in the world, covering roughly 30.2 million square miles that make up more than more than 17 percent of the world's airspace.3 Within that airspace, FAA air traffic controllers handle roughly 50,000 operations daily.4 As the demands on the air traffic system have changed over time, Congress and several presidential administrations have sought reforms to improve safety and efficiency and to accelerate modernisation projects. Over the past two decades, U.S. aviation stakeholders have debated whether the FAA should be the entity in the United States that operates and modernises the ATC system. During this period, the Government Accountability Office (GAO) reported on challenges FAA has faced in operating and modernising the ATC system. FAA reorganised several times in attempts to improve its performance and implement an initiative to modernise the ATC system, known as NextGen. Recent budgetary pressures have rekindled industry debate about FAA's efficiency in operating and modernising the ATC system. This book provides perspectives from a wide range of stakeholders on the performance of the ATC system and the NextGen modernisation initiative and any challenges FAA may face in managing these activities and potential changes that could improve the performance of the ATC system, including the NextGen modernisation initiative.