Operations research has been one of the principal contributors to the enor mous growth that the air transport sector has experienced during the past 50 years. In the best tradition of OR, the development of models and of solutions has been motivated by issues and problems encountered in practice and has led, in several instances, to insights of a general nature and to important methodological advances in the OR field at large. At this point, OR models and algorithms are diffused throughout the sector and constitute an integral part of the standard practices of airlines, airports, and ATM service providers