
Australasia was the name of a combined team at the 1912 Summer Olympics in Stockholm, Sweden, consisting of 26 athletes from Australia and New Zealand. The combined team had also competed at the 1908 Games, but Australia and New Zealand would send separate teams to the next Games in 1920.

Austria competed at the 1912 Summer Olympics in Stockholm, Sweden. Austrian and Hungarian results at early Olympic Games are generally kept separate despite the union of the two nations as Austria-Hungary at the time. 85 competitors, 76 men and 6 women, took part in 46 events in 12 sports.

Belgium competed at the 1912 Summer Olympics in Stockholm, Sweden.

Bohemia competed at the 1912 Summer Olympics in Stockholm, Sweden, for the last time. Beginning at the 1920 Olympic Games, Bohemian athletes would compete for the new nation of Czechoslovakia. Until 1918 Bohemia was part of Austria-Hungary.

Canada competed at the 1912 Summer Olympics in Stockholm, Sweden. 37 competitors, all men, took part in 30 events in 7 sports.

Chile competed at the 1912 Summer Olympics in Stockholm, Sweden. It was the first official appearance of the nation at the modern Olympic Games, although some sources claim that a single Chilean athlete competed at the 1896 Summer Olympics. Fourteen competitors, all men, took part in sixteen events in four sports.

Denmark competed at the 1912 Summer Olympics in Stockholm, Sweden. 152 competitors, 151 men and 1 woman, took part in 46 events in 13 sports.

The Egyptian Olympic Committee considers the nation to have first competed in the Summer Olympic Games at the 1912 Summer Olympics in Stockholm, Sweden. According to the official report, the nation sent one fencer, Ahmed Hassanein, who competed in the individual foil and épée events. There is uncertainty, however, as to whether he competed, as the official report lists all entrants in fencing regardless of their actual participation, and no results are known for Hassanein.

Finland competed at the 1912 Summer Olympics in Stockholm, Sweden. The Grand Duchy of Finland was part of the Russian Empire at the time, but Finland's results are kept separate from those of Russia. In the Opening Ceremony Finland's team paraded under the national insignia flag of a Swedish-speaking female gymnastics club in Helsinki. 164 competitors, 162 men and 2 women, took part in 49 events in 10 sports.

France competed at the 1912 Summer Olympics in Stockholm, Sweden. 119 competitors, 118 men and 1 woman, took part in 66 events in 13 sports.

Germany competed at the 1912 Summer Olympics in Stockholm, Sweden. 185 competitors, 180 men and 5 women, took part in 69 events in 14 sports. Due to the political fallout from World War I, this was that country's last appearance until 1928.

Great Britain, represented by the British Olympic Association (BOA), competed at the 1912 Summer Olympics in Stockholm, Sweden. 274 competitors, 264 men and 10 women, took part in 79 events in 16 sports. British athletes won ten gold medals and 41 medals overall, finishing third.

Greece competed at the 1912 Summer Olympics in Stockholm, Sweden. 22 competitors, all men, took part in 25 events in five sports. Greek athletes have competed in all Summer Olympic Games.

Hungary competed at the 1912 Summer Olympics in Stockholm, Sweden. Austrian and Hungarian results at early Olympic Games are generally kept separate despite the union of the two nations as Austria-Hungary at the time. 121 competitors, all men, took part in 52 events in 11 sports.

Iceland competed in the Summer Olympic Games for the first time at the 1912 Summer Olympics in Stockholm, Sweden. Olympic historians treat Iceland's results separate from those of Denmark despite Iceland's lack of independence at the time.

Italy competed at the 1912 Summer Olympics in Stockholm, Sweden.

The Empire of Japan competed at the Summer Olympic Games for the first time at the 1912 Summer Olympics in Stockholm, Sweden.

Luxembourg competed at the 1912 Summer Olympics in Stockholm, Sweden. It was the first official appearance at the modern Olympic Games for the nation, although it was later discovered that one Luxembourgish athlete competed in 1900.

Athletes from the Netherlands competed at the 1912 Summer Olympics in Stockholm, Sweden. 33 competitors, all men, took part in 14 events in 7 sports.

Norway competed at the 1912 Summer Olympics in Stockholm, Sweden. 190 competitors, 188 men and 2 women, took part in 58 events in 14 sports.

Portugal's first participation in the Summer Olympic Games took place at the 1912 Summer Olympics in Stockholm, Sweden. The nation was represented by a delegation of six competitors, who took part in three sports but failed to win a medal. The Portuguese debut participation was marked by the death of flag bearer Francisco Lázaro, who succumbed to serious dehydration after the marathon race.

Russian Empire (Russia) competed at the 1912 Summer Olympics in Stockholm, Sweden. 159 competitors, all men, took part in 62 events in 15 sports.

Serbia sent two athletes that competed in the 1912 Summer Olympics in Stockholm, Sweden. This was the first and only games where participated the Olympics as an independent nation until the 2008 Summer Olympics. By the next Olympic Games in 1920, Serbian athletes competed for the Kingdom of the Serbs, Croats and Slovenes, which in 1929 changed its name to Yugoslavia (YUG).

The Union of South Africa competed at the 1912 Summer Olympics in Stockholm, Sweden. 21 competitors, all men, took part in 21 events in 6 sports.

Sweden was the host nation for the 1912 Summer Olympics in Stockholm. 444 competitors, 421 men and 23 women, took part in 95 events in 16 sports.

Switzerland competed at the 1912 Summer Olympics in Stockholm, Sweden.

The Ottoman Empire competed at the 1912 Summer Olympics in Stockholm, Sweden.

The United States competed at the 1912 Summer Olympics in Stockholm, Sweden. 174 competitors, took part in 68 events in 11 sports. Out of the 174 athletes who had participated, 63 won medals.