Any international airport must necessarily have customs facilities, and often require a more perceptible level of physical security. This includes national police and custom agents, drug inspections, and, in general, any inspection to ensure migration and commerce regulations.
Airports are required to have security services in most countries. These services might be sublet to a private security company or carried out by the national security services of the country (sometimes, one would find a mixture between these two). Airport security normally requires baggage checks, metal screenings of individual persons, and rules against any object that could be used as a weapon. Since the September 11, 2001 attacks, airport security has been dramatically increased worldwide.
Airports, specially the largest international airports located in big cities, are often located next to highways or are served by their own highways. Traffic is fed into two access roads (loops) one sitting on top of the other to feed both departures and arrivals (typically in two different levels). Also, many airports have the urban rail system directly connecting the main terminals with the inner city. Very recently, to facilitate connections with medium distance cities (up to 500-600 [km]), there are projects (if is not a reality already) to incorporate the high speed train in the airport facility, connecting big capitals with other important cities.
Shop and food services
Every single airport, even the smallest ones, have shops and food courts (at least one little shop to buy a snack and soda). These services provide passengers food and drinks before they board their flights. If we move to large international airports, these resemble more like a shopping mall, with many franchise food places and the most well-known retail branches (specially clothes stores). International areas usually have a duty-free shop where travelers are not required to pay the usual duty fees on items. Larger airlines often operate member-only lounges for premium passengers (VIP lounges). The key of this business is that airports have a captive audience, sometimes with hours of layover in connections, and consequently the prices charged for food are generally much higher than elsewhere in the region.
Cargo and freight services
Airports are also facilities where large volumes of cargo are continuously moved throughout the entire globe. Cargo airlines carry out this business, and often have their own adjacent infrastructure to rapidly transfer freight items between ground and air modes of transportation.
Other services that provide support to airlines are aircraft maintenance, pilot services, aircraft rental, and hangar rental. At major airports, particularly those used as hubs by major airlines, airlines may operate their own support facilities. If this is not the case, every single company operating an airport must have access to the above mentioned services, which are typically rented on demand.