Mexico competed at the 2004 Summer Olympics in Athens, Greece, from 13 to 29 August 2004. This was the nation's twentieth appearance at the Olympics, since its debut in 1900. Comité Olímpico Mexicano sent the nation's largest delegation to the Games since 1992. A total of 109 athletes, 59 men and 50 women, competed in 20 sports. Football was the only team-based sport in which Mexico had its representation in these Olympic Games. There was only a single competitor in fencing, shooting, and weightlifting.
Nigeria competed at the 2004 Summer Olympics in Athens, Greece, from 13 to 29 August 2004. This was the nation's thirteenth appearance at the Olympics, except the 1976 Summer Olympics in Montreal, because of the African boycott. Nigerian Olympic Committee sent a total of 72 athletes, 24 men and 48 women, to the Games to compete in 10 sports. For the first time in its Olympic history, Nigeria was represented by more female than male athletes. Women's basketball and women's football were the only team-based sports in which Nigeria had its representation at these Games. There was only a single competitor in men's freestyle wrestling.
Canada, represented by the Canadian Olympic Committee (COC), competed at the 2012 Summer Olympics in London, United Kingdom, from 27 July to 12 August 2012. Canadian athletes have competed in every Summer Olympic Games since 1900, except the 1980 Summer Olympics in Moscow because of the country's support for the United States-led boycott. Canada sent a total of 281 athletes to the Games to compete in 24 sports. The COC set a goal of finishing in the top 12 for total medals; but the nation failed to achieve this, finishing with a total of 18 medals. Canada matched its total medal count from Beijing 2008. At London, with the initiation of its "Own the Podium" programme, Canada finished 13th in total medals, thus improving on its 14th place performance in Beijing while falling somewhat short of its self-declared goal of 12th position. It finished the event with 18 medals: two gold, six silver and 10 bronze.
Belarus competed at the 2012 Summer Olympics in London, United Kingdom, from 27 July to 12 August 2012. This was the nation's fifth appearance at the Summer Olympics in the post-Soviet era. The Belarus Olympic Committee sent a total of 166 athletes to the Games, 90 men and 76 women, to compete in 20 sports.
France competed at the 2012 Summer Olympics in London, between 27 July and 12 August 2012. French athletes have competed in every Summer Olympic Games of the modern era. The French Olympic Committee sent a total of 330 athletes to the Games, 183 men and 147 women, to compete in 24 sports.
Spain competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. This nation has competed in all but two Summer Olympic Games since its official debut in 1920. Spain boycotted two editions, the 1936 Summer Olympics in Nazi Germany and the 1956 Summer Olympics in Melbourne, as a protest against the Soviet invasion of Hungary. In 2012, the Spanish Olympic Committee sent the nation's smallest delegation to the Games since 1988. A total of 278 athletes, 166 men and 112 women, competed in 23 sports.
Japan, represented by Japanese Olympic Committee, competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. Despite being London's third Olympic Games, Japan marked their London debut at this games. The nation also celebrated its centennial anniversary in the Olympics, having participated at every games since 1912 except for two editions; it was not invited to the 1948 Summer Olympics in London for its role in World War II, and was also part of the US-led boycott of the 1980 Summer Olympics in Moscow. Japan sent a total of 295 athletes to the Games, 138 men and 157 women, to compete in 24 sports.
Brazil competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. This was the nation's twenty-first appearance at the Summer Olympics, having missed the 1928 Summer Olympics in Amsterdam. The Brazilian Olympic Committee sent a total of 258 athletes to the Games, 136 men and 122 women, to compete in 24 sports. Brazil left London with a total of 17 Olympic medals, winning their third largest number of medals at a single games.
New Zealand competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. This was the nation's twenty-fourth appearance at the Olympics. The New Zealand Olympic Committee sent 184 athletes, 97 men, and 87 women to the Games to compete in 16 sports, the nation's largest ever delegation.
Uruguay competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. This was the nation's twentieth appearance at the Olympics, Uruguay missed the 1980 Summer Olympics in Moscow, because of its partial support for the United States boycott.
Mexico competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. This was the nation's twenty-second appearance at the Olympics since its debut in 1900. Comité Olímpico Mexicano sent a total of 102 athletes to the Games, 64 men and 38 women, to compete in 23 sports. Men's football was the only team sport in which Mexico was represented at these Olympic Games. There was only a single competitor in badminton, sprint canoeing, and table tennis.
South Korea competed at the 2012 Summer Olympics in London, from July 27 to August 12, 2012. This was the nation's sixteenth appearance at the Olympics, having missed the 1980 Summer Olympics in Moscow because of its support for the United States boycott. The Korean Olympic Committee sent the nation's smallest delegation to the Games since 1992. A total of 248 athletes, 135 men and 113 women, competed in 22 sports.
North Korea competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. This was the nation's ninth appearance at the Olympics since its debut in 1972. North Korean athletes did not attend the 1984 Summer Olympics in Los Angeles, when they joined the Soviet boycott, and subsequently, led a boycott at the 1988 Summer Olympics in Seoul, along with six other nations.
Colombia competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. This was the nation's eighteenth appearance at the Olympics, having not competed at the 1952 Summer Olympics in Helsinki.
Sweden competed at the 2012 Summer Olympics in London, from 25 July to 12 August 2012. Swedish athletes have competed at every edition of the Summer Olympic Games in the modern era, except for the 1904 Summer Olympics in St. Louis. The Swedish Olympic Committee sent a total of 134 athletes to the Games, 55 men and 79 women, to compete in 20 sports. For the second consecutive time in its Olympic history, Sweden was represented by more female than male athletes.
Switzerland competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. Swiss athletes have competed at every Summer Olympic Games in the modern era, except when they boycotted the 1956 Summer Olympics in Melbourne in protest of the Soviet invasion of Hungary. The Swiss Olympic Association sent a total of 103 athletes to the 2012 Games, 72 men and 31 women, to compete in 18 sports.
Morocco competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. It was the nation's thirteenth appearance at the Olympics, having not participated at the 1980 Summer Olympics in Moscow because of its support of the United States boycott.
Senegal competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. This was the nation's thirteenth appearance at the Olympics.
Cameroon competed at the 2012 Summer Olympics in London, United Kingdom, from 27 July to 12 August 2012. This was the nation's thirteenth appearance at the Olympics.
Honduras competed at the 2012 Summer Olympics in London, United Kingdom, from 27 July to 12 August 2012. This was the nation's tenth appearance at the Olympics, excluding the 1972 Summer Olympics in Munich, and the 1980 Summer Olympics in Moscow, because of the American-led boycott.
