Top 30 world's busiest airports by international passenger traffic and top 50 world's busiest airports by passenger traffic.
Data are measured by total passengers (data from Airports Council International (ACI), defined as passengers enplaned plus passengers deplaned plus direct-transit passengers.
Hartsfield-Jackson International Airport in Atlanta has been the world's busiest airport every year since 2000; with all airports combined London has the world's busiest city airport system by passenger count. In 2013 there were 129 million passengers at London airports.
Data available from Airports Council International