Reliever airports hold a special place within the National Plan of Integrated Airport Systems (NPIAS) in the United States. Established in the 1960s, the purpose of reliever airports was to draw general aviation traffic away from congested primary airports located in larger metropolitan areas. In time, many of these airports evolved from simply relieving local air traffic congestion to functioning as both operational and economic hubs for the communities they serve. The purpose of this paper is to highlight the development of the reliever airport network in the United States and to explore their role (existing or potential) in the larger air transport system, as well as the associated regions that they serve. Specifically, a case study of the Phoenix Arizona metropolitan area and its reliever network is conducted. The results suggest that although many relievers are destined for their original purpose, others may have the opportunity to diversify their form and function.JEL classification: L93, R58, O21