Top ten world's busiest airports by passenger traffic are measured by number of total passengers (data provided by Airports Council International and BAA). One passenger is described as someone who arrives in, departs from, or transfers through the airport on a given day. Hartsfield-Jackson International Airport in Atlanta has been the world's busiest airport every year since 2000 whilst London has the world's busiest city airspace with 2 of its airports regularly found in the top ten.
Hartsfield-Jackson Atlanta International Airport - Georgia, United States

Total Passenger: 20,181,931
O'Hare International Airport - Chicago, Illinois, United States

Total Passenger: 15,346,475
London Heathrow Airport - United Kingdom

Total Passenger: 15,268,609
Tokyo International Airport - Japan

Total Passenger: 15,180,894
Beijing Capital International Airport - China

Total Passenger: 15,153,600
Dallas-Fort Worth International Airport - Texas, United States

Total Passenger: 12,833,031
Los Angeles International Airport - California, United States

Total Passenger: 12,630,858
Paris-Charles de Gaulle Airport - France

Total Passenger: 12,447,664
Denver International Airport - Colorado, United States

Total Passenger: 11,495,033
Hong Kong International Airport - Chek Lap Kok, Hong Kong

Total Passenger: 11,098,500

Total Passenger: 20,181,931
O'Hare International Airport - Chicago, Illinois, United States

Total Passenger: 15,346,475
London Heathrow Airport - United Kingdom

Total Passenger: 15,268,609
Tokyo International Airport - Japan

Total Passenger: 15,180,894
Beijing Capital International Airport - China

Total Passenger: 15,153,600
Dallas-Fort Worth International Airport - Texas, United States

Total Passenger: 12,833,031
Los Angeles International Airport - California, United States

Total Passenger: 12,630,858
Paris-Charles de Gaulle Airport - France

Total Passenger: 12,447,664
Denver International Airport - Colorado, United States

Total Passenger: 11,495,033
Hong Kong International Airport - Chek Lap Kok, Hong Kong

Total Passenger: 11,098,500