Greece was the host country for the 2004 Summer Olympics in Athens, from 13 to 29 August 2004. As the progenitor nation and in keeping with tradition, Greek athletes have competed at every Summer Olympics in the modern era, alongside Australia, Great Britain, and Switzerland. The Hellenic Olympic Committee fielded a total of 426 athletes to the Games, 215 men and 211 women, and had achieved automatic qualification places in all sports, with the exception of men's and women's field hockey. It was also the nation's largest team ever in Summer Olympic history since the first modern Games were held in 1896.
Japan competed at the 2004 Summer Olympics in Athens, Greece, from 13 to 29 August 2004. Japanese athletes have competed at every Summer Olympic Games in the modern era 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. The Japanese Olympic Committee sent a total of 306 athletes, 139 men and 167 women, to compete in 27 sports. For the first time in its Olympic history, Japan was represented by more female than male athletes.
Portugal competed at the 2004 Summer Olympics in Athens, Greece, from 13 to 29 August 2004. Portuguese athletes have competed at every Summer Olympic Games in the modern era since 1912. The Olympic Committee of Portugal sent the nation's second-largest team to the Games. A total of 81 athletes, 64 men and 17 women, were selected by the committee to participate in 15 sports. Men's football was the only team-based sport in which Portugal had its representation at these Games. There was only a single competitor in badminton, canoeing, equestrian, artistic and trampoline gymnastics, triathlon, and wrestling, which made its official Olympic comeback after an eight-year absence.
France competed at the 2004 Summer Olympics in Athens, Greece, from 13 to 29 August 2004. French athletes have competed in every Summer Olympic Games of the modern era. The French Olympic Committee sent a total of 308 athletes to the Games, 195 men and 113 women, to compete in 25 sports.
Italy competed at the 2004 Summer Olympics in Athens, Greece, from the 13th to the 29th of August 2004. The country 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 largest ever delegation in history to the Games. A total of 364 athletes, 229 men and 135 women, competed in 27 sports.
Germany competed at the 2004 Summer Olympics in Athens, Greece, from 13 to 29 August 2004. This was the nation's fourth consecutive appearance at the Summer Olympics after its reunification in 1990. The German Olympic Sports Confederation sent the nation's second largest delegation to the Games since its reunification. A total of 441 athletes, 250 men and 191 women, competed in 27 sports, and were nominated by DOSB at four occasions.
Poland competed at the 2004 Summer Olympics in Athens, Greece, from 13 to 29 August 2004. This was the nation's eighteenth appearance at the Summer Olympics, except the 1984 Summer Olympics in Los Angeles, because of the Soviet boycott. The Polish Olympic Committee sent a total of 194 athletes to the Games, 132 men and 62 women, to compete in 21 sports. Men's volleyball was the only team-based sport in which Poland had its representation in these Olympic Games. There was only a single competitor in women's taekwondo.
Spain competed at the 2004 Summer Olympics in Athens, Greece, from August 13 to 29, 2004. This nation has competed in every Summer Olympic Games since its official debut in 1920. Spain, however, boycotted two editions, the 1936 Summer Olympics in Nazi Germany, and the 1956 Summer Olympics in Melbourne when it joined the Dutch-led boycott, as a protest to the Soviet invasion of Hungary. The Spanish Olympic Committee sent the nation's third largest delegation in history to the Games. A total of 317 athletes, 177 men and 140 women, competed in 26 sports.
Czech Republic competed at the 2004 Summer Olympics in Athens, Greece, from 13 to 29 August 2004. This was the nation's third appearance at the Summer Olympics after gaining its independence from the former Czechoslovakia. The Czech Olympic Committee sent the nation's largest team to the Games since the post-Czechoslovak era. A total of 142 athletes, 80 men and 62 women, competed in 19 sports; the nation's team size was roughly denser from Sydney by one sixth of the athletes. Women's basketball was the only team-based sport in which the Czech Republic had its representation at these Olympic Games. There was only a single competitor in equestrian, artistic and trampoline gymnastics, judo, and weightlifting.
Argentina competed at the 2004 Summer Olympics in Athens, Greece, from 13 to 29 August 2004. This was the nation's twenty-first appearance at the Olympic Games, except for three different editions. Argentina did not attend the 1904 Summer Olympics in St. Louis, the 1912 Summer Olympics in Stockholm, and the 1980 Summer Olympics in Moscow, because of its support for the United States-led boycott. The sailor Carlos Espínola was the nation's flag bearer at the opening ceremony. 152 competitors, 106 men and 46 women, took part in 86 events in 22 sports.
Angola competed at the 2004 Summer Olympics in Athens, Greece from 13 to 29 August 2004.
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.
Serbia and Montenegro competed at the 2004 Summer Olympics in Athens, Greece, from 13 to 29 August 2004. Previously known as the Federal Republic of Yugoslavia, this was the nation's third and last joint appearance at the Summer Olympics before Serbia and Montenegro became separated independent states in 2006. The Olympic Committee of Serbia and Montenegro sent a total of 85 athletes to the Games, 78 men and 7 women, to compete in 14 sports. Men's basketball, football, volleyball, and water polo were the only team-based sports in which Serbia and Montenegro had its representation at these Games. There was only a single competitor in road cycling, judo, tennis, and wrestling.
Croatia competed at the 2004 Summer Olympics in Athens, Greece, from 13 to 29 August 2004. This was the nation's fourth consecutive appearance at the Summer Olympics since the post-Yugoslav era. The Croatian Olympic Committee sent the nation's smallest delegation to the Games since its debut in 1992. A total of 81 athletes, 66 men and 15 women, competed in 14 sports. Men's water polo, and men's handball were the only team-based sports in which Croatia had its representation in these Olympic Games.
Lithuania competed at the 2004 Summer Olympics in Athens, Greece, from 13 to 29 August 2004. This was the nation's sixth appearance at the Summer Olympics. The National Olympic Committee of Lithuania sent the nation's smallest delegation to the Games since the 1992 Summer Olympics in Barcelona. A total of 59 athletes, 47 men and 12 women, competed in 13 sports, including the men's basketball team as the nation's team-based sport.
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.
The United States of America (USA) competed at the 2004 Summer Olympics in Athens, Greece. 533 competitors, 279 men and 254 women, took part in 254 events in 31 sports.
Puerto Rico competed at the 2016 Summer Olympics in Rio de Janeiro, Brazil, from 5 to 21 August 2016. This was the nation's eighteenth consecutive appearance at the Summer Olympics.
Puerto Rico 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 territory's nineteenth consecutive appearance at the Summer Olympics. Like on the 2016 Summer Olympics, Puerto Rico left the Olympics with a single gold medal, this time won by Jasmine Camacho-Quinn. Other athletes fell short of their Olympic medal, with Steven Piñeiro finishing sixth in the men's skateboarding street park final, and table tennis player Adriana Díaz losing a match in the third round.
Puerto Rico competed at the 2024 Summer Olympics in Paris from 26 July to 11 August 2024. It was the territory's twentieth consecutive appearance at the Summer Olympics.
