Which is the busiest airport in the world: Chicago's O'Hare, or Atlanta's Hartsfield-Jackson International? Depends on how you define "busiest," according to the FAA. O'Hare has handled the most number of flights in the first half of 2004 (nearly a half-million), but Hartsfield-Jackson is handling the most number of passengers (12 million in the first 4 months of 2004). Either way, that's still a huge amount of traffic flowing through the two airports. We'll have to check back with this story near the end of the year, to see which airport will win the coveted title of World's Busiest Airport. (I think there might be a trophy of some sort awarded to the winner.)