There are winter Olympics so people with winter sports interest can compete in the games. eg. Skiing, figure skating. Summer Olympics so people with summer sports can compete in the games. Gymnastics, swimming...ect.
The only sport the US does not compete in at any Summer Olympics (including 2008 and the upcoming 2012) is handball.
The Australian Olympic Committee sent a total of 410 athletes to the Games to compete in 23 sports.
Iceland is sending athletes to the 2008 Summer Olympics to compete in Athletics, Badminton, Handball, Judo, and Swimming.
Mauritius competed in the following sports in the 2008 Olympics:400m DashArcheryBadmintonBoxingCyclingSwimmingWeightlifting
Georgia is sending 35 athletes to compete in 10 sports at the 2008 Summer Olympics. The sports the Georgian athletes will compete in are Archery, Athletics, Swimming, Boxing, Gymnastics, Judo, Shooting, Volleyball, Weightlifting, and Wrestling.
People are chosen to compete in the Olympics by competing in the Olympic Trials. In most sports, the top competitors from the Olympic Trials are chosen to compete in the Olympics.
The United States Olympic Committee sent a total of 539 athletes to the Olympics in London to compete in 25 sports. London Summer Olympics 2012
Currently (in 2009) there are 26 summer sports.
There are many, many sports that have not been events in the Olympics