Hartsfield-Jackson Atlanta, USA
Hartsfield-Jackson has been the world's busiest airport for the past 15 years, and is the biggest hub airport in the United States.
Seen from the air, this picture was taken by Daniel Betts.
92,389,023 passengers travel through the airport in 2011
The airport is the largest employer in the state of Georgia - 58,000 airline staff work in the vast complex
The airport boast six runways
Beijing Capital, China
Beijing Capital International Airport is the main international airport serving Beijing. It has been Asia's busiest airport since 2009.
78,675,058 passengers travelled through the airport in 2011
In 2008, it added an enormous Terminal 3 in time for the Olympic Games, the second largest airport terminal in the world, after Dubai's International Terminal 3
London Heathrow, UK
Heathrow Airport is Europe's busiest hub airport, where 84 airlines operate flights to 184 destinations in 80 countries.
69,433,565 passengers travelled through Heathrow Airport in 2011
An average of 191,200 passengers arrive and depart from the airport every day
The airport has five terminals
Chicago O'Hare, USA
Chicago O'Hare is the second biggest hub in the United States, and until 2005 was the world's busiest airport in terms of takeoffs and landings.
66,701,241 passengers travelled through the airport in 2011
It employs 41,300 employees
50 airlines fly to 198 destinations from the hub
Tokyo International, Japan
Haneda Airport is one of the two primary airports that serve the Greater Tokyo area. It is the second busiest airport in Asia, and has four runways.
62,584,826 passengers travelled through the airport in 2011
Haneda is the third-largest air cargo hub in Japan after Narita and Kansai.
The passenger numbers are counted as the total number who board and depart and passengers in transit are counted once.