From the IOC's website: "In Beijing more than 10'500 athletes from 204 NOCs will be present at the Games" http://www.olympic.org/uk/utilities/faq_selection_new_uk.asp
Under the question "How many countries...?"
The number of countries participating in the Beijing Olympic Games of 2008 was 205.
Mexico sent 85 athletes to compete at the 2008 Games.
Great Britain sent 311 athletes to compete at the 2008 Games in Beijing.
According to London2012 site there are 289 Italian athletes participating in the 2012 Olympics.
647
11,028 athletes from 204 countries are participating at the 2008 Games.
There were 204 countries participating in the Olympic games in which 86 of these won medals
45 country are participating in Asia games 2010
so many of them are participating
Luxembourg sent a team of 13 athletes to compete at the 2008 Games in Beijing in cycling, triathlon, tennis, judo, gymnastics, swimming, and sailing. No athlete from Luxembourg won a medal at the 2008 Games.
there are approximately 1000 people participating in common wealth games.
Puerto Rico has qualified athletes in boxing and women's weightlifting for the 2008 Games.