Rio beat out Madrid, Spain, in the final round. Chicago, Illinois, and Tokyo, Japan, were eliminated in earlier rounds.
For Rio, a major appeal was bringing the Olympics to South America for the first time.
IOC President Jacques Rogge said in the news conference afterward that in addition to its excellent bid, Rio had the "extra-added value of going for the first time to a continent that's never had the Games."
He also noted that Brazil helped its chances this year when it did not get the 2012 Games awarded four years ago.
[coverattach=2]"Rio remained humble," he said. "They wanted to listen, to repair their shortcomings."
More than half of Rio's Olympic venues are built, including state-of-the-art facilities constructed for the 2007 Pan and Parapan American Games: the magnificent Joao Havelange Stadium (the proposed 2016 venue for athletics), the Maria Lenk Aquatic Center, the Rio Olympic Arena (which will host gymnastics and wheelchair basketball), the Rio Olympic Velodrome, the National Equestrian Center and its close neighbor, the National Shooting Center.