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.
Water polo at the World Aquatics Championships is an international water polo tournament held every two years as part of the World Aquatics Championships. The reigning champions are Croatia in men's and the United States in women's competition.
Water polo has been part of the Summer Olympics program since the second games, in 1900. A women's water polo tournament was introduced for the 2000 Summer Olympics. Hungary has been the most successful country in men's tournament, while the United States is the only team to win multiple times at the women's tournament since its introduction. Italy is the first and only country to win both the men's and women's water polo tournaments.
The Greece men's national water polo team represents Greece in international men's water polo competitions and it is organized and run by the Hellenic Swimming Federation.
The 2012 Men's European Water Polo Championship took place at the Pieter van den Hoogenband Swim Stadium in Eindhoven, the Netherlands, from 16 to 29 January 2012.
The men's water polo tournament at the 2011 World Aquatics Championships, organised by the FINA, was held in Shanghai, China from 18 to 30 July 2011.
The women's water polo tournament at the 2011 World Aquatics Championships, organised by the FINA, was held in Shanghai, China from 17 to 29 July 2011.
Brazil was the host nation of the 2016 Summer Olympics in Rio de Janeiro from 5 to 21 August 2016. This was the nation's twenty-second appearance at the Summer Olympics, having competed in all editions in the modern era from 1920 onwards, except the 1928 Summer Olympics in Amsterdam. Setting a milestone in Olympic history, Brazil became the first South American country to host the Summer Olympics, and the second Latin American host following the 1968 Summer Olympics in Mexico.
The 2012 Men's Water Polo Olympic Qualification Tournament was held at the Kinsman Sports Centre in Edmonton, Alberta, Canada, from 1 to 8 April 2012.
The 2012 Women's Water Polo Olympic Qualification Tournament was held at the Polo Natatorio Bruno Bianchi in Trieste, Italy, from 15 to 22 April 2012.
The women's water polo tournament at the 2013 World Aquatics Championships, organised by the FINA, was held in the Piscines Bernat Picornell in Barcelona, Spain from 21 July to 2 August 2013.
Croatia competed at the 2016 Summer Olympics in Rio de Janeiro, Brazil, from 5 to 21 August 2016. This was the nation's seventh consecutive appearance at the Summer Olympics. The Croatian Olympic Committee confirmed a roster of 87 athletes, 68 men and 19 women, to compete across 18 sports at the Games.
The men's water polo tournament at the 2017 World Aquatics Championships, organised by the FINA, was held in Budapest, Hungary from 17 to 29 July 2017.
Japan was the host nation of the 2020 Summer Olympics in Tokyo, originally scheduled to take place from 24 July to 9 August 2020 but postponed to 23 July to 8 August 2021 because of the COVID-19 pandemic. Since the nation's official debut in 1912, Japanese athletes have appeared at every Summer Olympic Games in the modern era, except for the 1948 Summer Olympics in London, to which they were not invited due to the nation's role in World War II, and the 1980 Summer Olympics in Moscow, as part of the United States-led boycott. The opening ceremony flag-bearers for Japan are basketball player Rui Hachimura and wrestler Yui Susaki. Karateka Ryo Kiyuna is the flag-bearer for the closing ceremony.
The qualification for the 2020 men's Olympic water polo tournament allocated twelve teams quota spots: the hosts, the top team in the World League, the top two teams in the World Championships, five continental Olympic qualification tournament champions, and the three top teams at an Olympic qualifying tournament.
The qualification for the 2020 women's Olympic water polo tournament allocated ten teams quota spots: the hosts, the top team in the World League, the top team in the World Championships, five continental Olympic qualification tournament champions, and the two top teams at an Olympic qualifying tournament.
Spain competed at the 2020 Summer Olympics in Tokyo, originally scheduled to take place from 24 July to 9 August 2020 but postponed to 23 July to 8 August 2021 because of the COVID-19 pandemic. Since the nation's official debut in 1920, Spanish athletes have appeared in every edition of the Summer Olympic Games, with the exception of the 1936 Summer Olympics in Berlin and the 1956 Summer Olympics in Melbourne, as a part of the boycott against the Soviet invasion of Hungary. Spain competed in all sports except baseball, rugby sevens, wrestling and surfing.
The Netherlands 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. Dutch athletes have competed at every edition of the Summer Olympic Games, with the exception of the sparsely attended 1904 Summer Olympics in St. Louis and 1956 Summer Olympics in Melbourne, which the Netherlands boycotted because of the Soviet invasion of Hungary.
Spain (in Barcelona host cities)
Hungary (3rd title)
Montenegro 
Croatia 
Italy 
