The airline industry can been described as one of the most technologically advanced. The primary players—the scheduled carriers rely on a wide variety of management information systems and decision support systems, which are typically developed using concepts from operations research and artificial intelligence. Operation research techniques have been applied to all areas of airline management, ranging from the strategic planning phase through to the post-analysis phase of operations. We present the state-of-the-art in the airline industry as it relates to applying operations research to solve traditional airline planning problems. We describe each business problem, review existing solution procedures, highlight recent research activity, and identify potential advancements and research opportunities. In addition, we quantify the benefits of implementing operations research based solutions in the airline industry. been transformed into a highly competitive environment marked by a rapid growth in the number of low-cost carriers entering the mar- ket. This fact has forced U.S. major network carriers to reengineer business practices in many functional areas, from the introduction of revenue management, the restructuring of their flight network, to the development of centralized airline operations control centers. This phenomenon has spread to other parts of the world and is now playing out in the intra-European market. One of the major outcomes of the deregulation in the U.S. do- mestic market was the development of hub-and-spoke networks. Hub airports have developed at strategically located cities and are used as transfer points for passengers traveling from one commu- nity to another in the region surrounding the hub airport. They also serve as collection nodes for passengers traveling to and from the nearby communities to international gateways and other parts of the country. As a result, airlines can now provide service to more origin-destination markets. Typically carriers schedule a series of banks of flights into and out of their hub airports over the course of the day. Each bank normally consists of 20 plus aircraft arriv- ing within minutes of each other, followed by a short period of no aircraft movement, and then the departure of all aircraft at the hub to their final destination. While the aircraft are on the ground, con- necting passengers arriving on in-bound flights can transfer to their outbound flights within the prescribed connecting time. From an airline planning perspective the hub-and-spoke network has given carriers the opportunity to better manage the use of their limited re- sources, in particular aircraft and crew members. At the same time it has substantially increased the complexity of aircraft routing and crew scheduling, as the number of possible feasible solutions will increase because of the combinatorial nature of a highly connected