All but three of the 196 independent countries of the world are participating in the Olympic Games, thus there are 193 independent countries participating in the 2012 Summer Olympic Games in London.
In addition to the 193 independent countries, there are eleven territories or other entities that have been permitted by the International Olympic Committee to have their own National Olympic Committee (NOC). By having an independent NOC, each of these eleven places is able to compete in the Olympic Games and plans on sending athletes to London for the 2012 Summer Games there.
Thus, the total of 193 independent countries and 11 territories equals the number 204 that is being thrown about as the number of "countries" competing in the Summer Games.
Three Independent Countries Not Participating in the Olympic Games
South SudanSouth Sudan is the world's newest country. South Sudan became independent from Sudan last year, in July 2011. South Sudan quickly became a member of the United Nations in 2011, enabling the country to establish a National Olympic Committee. Unfortunately, the war-torn country has been unable to develop a NOC in the short time since independence so the country's few athletes will not be able to compete in London.
KosovoKosovo is the world's second newest country and does not yet have complete international recognition. Even though Kosovo established their Olympic Committee of Kosovo (OCK) in 2003 and declared independence in 2008, their ongoing dispute with Serbia as to their status has prevented Kosovo from having an official National Olympic Committee and thus Kosovars are unable to participate in the 2012 Summer Games.
Vatican City/Holy SeeDespite its internationally recognized independence, the Vatican City does not have a National Olympic Committee and has not publicized any aspirations to form one in order to compete in the Olympic Games.
Non-Countries Participating in the Olympic GamesThese are the eleven non-countries participating in the 2012 Summer Games. These entities have National Olympic Committees and therefore are able to participate in the Olympic Games. I have included the reason that each entity is not a country in parenthesis.
American Samoa (American Samoa is a territory of the United States)
- Aruba (Aruba part of the Netherlands, located in the Caribbean)
- Bermuda (Bermuda is a territory of the United Kingdom)
- British Virgin Islands (the British Virgin Islands is a territory of the United Kingdom)
- Cayman Islands (the Cayman Islands is a territory of the United Kingdom)
- Cook Islands (the Cook Islands is a self-governing in free association with New Zealand)
- Guam (Guam is a territory of the United States)
- Hong Kong (since 1997, Hong Kong has been a special administrative region of China)
- Palestine (Palestine is not yet a country.)
- Puerto Rico (Puerto Rico is a territory of the United States)
- U.S. Virgin Islands (the U.S. Virgin Islands is a territory of the United States)
Two Interesting NOC CasesOn an interesting note, the territory formerly known as Netherlands Antilles was dissolved in 2010 and subsequently lost its status as an official National Olympic Committee in 2011.
Unfortunately, for the 2008 Summer Games in Beijing, Brunei was unable to register their two athletes on time and therefore did not participate in the Summer Games. Fortunately, they have managed to field a team for the 2012 Summer Games in London!