The most advanced OR work on aviation infrastructure to date is undoubtedly associated with air traffic flow management (ATFM). ATFM took on major importance in the United States and Europe during the 1980s, when rapid traffic growth made it necessary to adopt a more strategic perspective on ATM. Rather than addressing congestion through local measures (e.g., by holding arriving aircraft in the airspace near delay-prone airports) the goal of ATFM is to prevent local system overloading by dynamically adjusting the flows of aircraft on a national or regional basis. It develops flow plans that attempt to dynamically match traffic demand with available capacity over longer time horizons, typically extending from 3–12 hours in the future. The prototypical application of ATFM is in ground holding, i.e., in intentionally delaying an aircraft’s takeoff for a specified amount of time to avoid airborne delays and excessive controller workload later on. Other ATFM tactics include rerouting of aircraft and metering (controlling the rate) of traffic flows through specified spatial boundaries in airspace. An important difference in the nature of the ATFM problem in the United States and in Europe should also be noted. In the United States, ATFM is primarily driven by airport capacity constraints, whereas in Europe en route airspace acts as the principal “bottleneck.” Europe’s Central Flow Management Unit, located in Brussels, currently determines (heuristically) ground delays to ensure that no en route sector capacity constraints are violated. This difference may, however, become moot in the near future due to continuing progress in increasing en route airspace capacity in Europe. OR model development related to ATFM can be viewed as going through two distinct stages. The first stage involved problem definition and development of large-scale mathematical optimization models of an aggregate scope. Attwool (1977) was the first to cast ATFM issues in mathematical terms, while