There are 206 National Olympic Committees competing at the Tokyo Olympics, and while the acronyms of most will be pretty obvious, there are others who aren't quite as straightforward by their shortened name alone.
Here's a look at a few of them.
Who are ROC and why can Russia compete despite sports ban?
Russian athletes are competing at the Tokyo Olympics
That's despite Russia being banned from competing due to a doping scandal, with the country denying any involvement in state-sponsored doping.
Russian athletes were banned from the 2018 Winter Olympic Games and banned from competing as a country in athletics competitions from 2015, and then Russia as a whole was blocked from competing at the Tokyo Olympics by the World Anti-Doping Agency (WADA) in 2019 for cover-ups in drugs testing.
The ban is currently scheduled to end in December 2022.
You may wonder, then, how on earth Russian athletes are competing in Japan.
It's all down to the fact they're representing the Russian Olympic Committee - a separate team entity. It features 335 Olympic athletes who have been able to show they were not involved in Russia's doping scandal.
Athletes are not allowed to have the Russian national anthem played or fly the Russia flag if they win a medal, while the ROC's flag must be different to Russia's and kit must have the letters 'ROC' on it instead of 'Russia' or 'Russian Olympic Committee'.
If 'Russia' is on their kit, the words 'neutral athlete' must also be included. Russian flag colours may be used.
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Who is in the Refugee Olympic Team?
The Refugee Olympic Team is made up of athletes from 11 countries, and there is also a team for the Paralympics for the first time.
The Tokyo Olympics is the second Games where such a team has competed at a Summer Games, with Rio 2016 marking the first time.
Since then, the team has grown from 10 to 29 members, who now live in 13 different countries.
They are from Syria, the Democratic Republic of Congo, South Sudan, Eritrea, Venezuela, Iran, Afghanistan, and Cameroon.
The team is competing in 12 sports: athletics, badminton, boxing, canoeing, cycling, judo, karate, taekwondo, shooting, swimming, weightlifting, and wrestling.
It's a success story since the International Olympic Committee launched a Refugee Emergency Fund in 2015 to try and encourage refugees into sport.
What country is TPE in the Olympics?
The acronym TPE stands for Chinese Taipei.
Taiwan has been competing under the name Chinese Taipei since the 1984 Los Angeles Olympics, but it has been competing under several different names since 1956.
The National Olympic Committee competed under the name Republic of China between 1956 and 1972, and after missing the 1976 and 1980 Games it returned in 1984 under the name Chinese Taipei.