Airports fulfill important infrastructural functions. Their main purpose is to provide infrastructure relevant to air transport. This mainly includes the provision of runway systems, passenger terminals, and connections to ground transport systems (see Fig. 4.1). Airports can be subdivided into landside and airside areas as well as air freight buildings. The terminal is the main landside building. In general it consists of two areas separated by border and passport control through which all passengers and flight personnel need to pass preflight. Check-in (ticket collection, seat reservation, luggage check-in, security control) takes place in the front part of the terminal.