Iran competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. The nation has competed at every Summer Olympic games since its official debut in 1948 with the exception of the 1980 and 1984 Summer Olympics. The National Olympic Committee of the Islamic Republic of Iran sent the nation's second-largest delegation to the Games, one less than it sent to Beijing. A total of 53 athletes, 45 men and 8 women, competed in 14 sports. This was also the youngest delegation in Iran's Olympic history, with half the team under the age of 25, and many of them are expected to reach their peak in time for the 2016 Summer Olympics in Rio de Janeiro. Heavyweight boxer Ali Mazaheri was the nation's flag bearer at the opening ceremony.
Estonia competed at the 2012 Summer Olympics in London, United Kingdom from 27 July to 12 August 2012. This was the nation's eleventh appearance at the Summer Olympics.
Uzbekistan competed at the 2012 Summer Olympics in London, from July 27 to August 12, 2012. This was the nation's fifth consecutive appearance at the Olympics. The National Olympic Committee of the Republic of Uzbekistan sent the nation's smallest delegation to the Games in the post-Soviet era. A total of 54 athletes, 36 men and 18 women, competed in 13 sports. There was only a single competitor in fencing, rhythmic and trampoline gymnastics, shooting and tennis.
Italy competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. This nation has competed at every Summer Olympic games in the modern era, except for the 1904 Summer Olympics in St. Louis. The Italian National Olympic Committee sent the nation's smallest delegation to the Games since the 1988 Summer Olympics in Seoul. A total of 285 athletes, 162 men and 123 women, competed in 22 sports.
Hungary competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. Hungarian athletes have competed at every Summer Olympic Games in the modern era, except the 1920 Summer Olympics in Antwerp, and the 1984 Summer Olympics in Los Angeles because of the Soviet boycott. The Hungarian Olympic Committee sent the nation's smallest delegation to the Games since 1956. A total of 159 athletes, 97 men and 62 women, competed in 18 sports.
Ukraine competed at the 2012 Summer Olympics in London, from July 27 to August 12, 2012. This was the nation's fifth consecutive appearance at the Summer Olympics in the post-Soviet era. The National Olympic Committee of Ukraine sent a total of 238 athletes, split equally between men and women, to compete in 21 sports.
Bulgaria competed at the 2012 Summer Olympics in London, United Kingdom from 27 July to 12 August 2012. It was the nation's nineteenth appearance at the Summer Olympics, having missed the Olympics on three occasions, including the 1984 Summer Olympics in Los Angeles because of the Soviet boycott. Despite this being London's third Olympic Games, this was the first time a Bulgarian team appeared at a London Olympics. The Bulgarian Olympic Committee sent the nation's smallest delegation to the Games, tying the record with Helsinki in 1952, and with Tokyo in 1964. A total of 63 athletes, 36 men and 27 women, competed in 16 sports. Men's volleyball was the only team event in which Bulgaria was represented in these Olympic games. There was only a single competitor in badminton, sprint canoeing, fencing, and judo.
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.
Cuba competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. This was the nation's nineteenth appearance in the Olympics. With baseball's removal from the Olympic program and the absence of the nation's volleyball team for the first time, the Cuban Olympic Committee sent the nation's smallest delegation to the Games since 1964. A total of 111 athletes, 66 men and 45 women, competed in 13 sports. There was only a single competitor in archery and table tennis.
Greece competed at the 2012 Summer Olympics in London, United Kingdom, from 27 July to 12 August 2012. The Hellenic Olympic Committee sent a total of 103 athletes to the Games in London, 65 men and 38 women, to compete in 19 sports. Men's water polo was the only team event in which Greece was represented at these Olympic Games.
Mongolia competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. This was the nation's twelfth appearance at the Olympics, except the 1984 Summer Olympics in Los Angeles, because of its partial support to the Soviet boycott.
Ecuador competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. This was the nation's twelfth consecutive appearance at the Olympics. It had first competed at the 1924 Summer Olympics in Paris.
Puerto Rico competed at the 2012 Summer Olympics in London, United Kingdom from July 27 to August 12, 2012. This was the nation's seventeenth consecutive appearance at the Olympics.
Nigeria competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. This was the nation's fifteenth appearance at the Olympics. Nigeria missed the 1976 Summer Olympics in Montreal because of the African boycott. The Nigerian Olympic Committee sent the nation's smallest delegation to the Games since 1984. A total of 53 athletes, 30 men and 23 women, competed in 8 sports. Men's basketball was the only team-based sport in which Nigeria was represented at these Olympic Games. Among the eight sports played by the athletes, Nigeria marked its official Olympic debut in slalom canoeing.
Tajikistan competed at the 2012 Summer Olympics in London, from 27 July to 12 August 2012. This was the nation's fifth consecutive appearance at the Olympics. The National Olympic Committee of the Republic of Tajikistan sent the nation's largest delegation to the Games. A total of 16 athletes, 13 men and 3 women, competed in 7 sports. Six of these athletes had competed in Beijing, including judoka Rasul Boqiev and freestyle wrestler Yusup Abdusalomov, who both won Tajikistan's first ever Olympic medals.
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.
Venezuela competed at the 2012 Summer Olympics in London, from July 27 to August 12, 2012. This was the nation's seventeenth consecutive appearance at the Olympics, since its debut at the same host city in 1948. Celebrating the anniversary of the nation's Olympic debut, the British Embassy in Caracas invited former track cyclist Julio César León to travel back to the United Kingdom, and revisit his memories as the first Venezuelan athlete in history to compete at the games.
Kyrgyzstan competed at the 2012 Summer Olympics in London, United Kingdom from 27 July 2012 to 12 August 2012. This was the nation's fifth appearance at the Olympics in the post-Soviet era.
Moldova, officially the Republic of Moldova, competed at the 2016 Summer Olympics in Rio de Janeiro, Brazil, from 5 to 21 August 2016. This was the nation's sixth consecutive appearance at the Summer Olympics in the post-Soviet era.
Moldova, officially the Republic of Moldova, competed at the 2020 Summer Olympics in Tokyo. Originally scheduled to take place from 24 July to 9 August 2020, the Games were postponed to 23 July to 8 August 2021, because of the COVID-19 pandemic. It was the nation's seventh consecutive appearance at the Summer Olympics in the post-Soviet era.
Russian Empire (1900–1912)
Romania (1924–1936)
Soviet Union (1952–1988)
Unified Team (1992)
