
Hartsfield–Jackson Atlanta International Airport
Located in Atlanta, Georgia, United States it is ranked as the biggest airport by most passengers annually and most flights (1998 – present).

Beijing Capital International Airport, Beijing, China

The city of Beijing has grown in pace with the development of the Chinese economy and it’s airport has flourished in recent times. The State carrier Air China uses the airport as its primary hub. The number of annual passengers is over 80 million and the Airport serves around 200 international destinations.
An interesting fact is that the gigantic Terminal 3 is the sixth-largest building in the world. Beijing is currently building a second airport which is expected to increase the passenger handling capacity of the city’s airports to 150 million.
Heathrow Airport, London, England, United Kingdom

London Heathrow Airport is the airport in the world with most international passengers passing through each year. About 75 million passengers land and take off on the two cramped runways year. Europeans travelling west towards North America, Central America, the Caribbean or South America often makes a stopover at London’s Heathrow Airport. If at all possible you should really try to avoid it as it is overcrowded, understaffed and crammed with security checkpoints.
Heathrow which began life as a small rural airstrip became the international hub for London during World War 2 where it was expanded for serving long distance military craft heading for the Far East. By the time it was nearly finished, the war ended and the airport was used for civilian purposes instead.
Honorable mention: Hong Kong International Airport, Hong Kong SAR

Built entirely on reclaimed land, it is the biggest airport in the world in terms of cargo transport. It handled more than 400.000 flights and massive 4.4 million tons of cargo in 2015. The location and political status of Hong Kong makes the entry port into China for most of the worlds cargo, both on land and sea.