The IOI 2021 Organising Committee has invited all qualifying teams to participate in IOI 2021.
Team leaders with access to the IOI 2021 registration system have registered their teams.
THUS, REGISTRATION IS NOW CLOSED
For future years, countries and regions that wish to compete in IOI for the first time (or returning after more than three years of absence) will need to (re-)register as members of the IOI Foundation before participating. To do so, please contact the IOI acting secretary, Prof Benjamin Burton, at secretary.ioinformatics@gmail.com for details.
| No | Team | GMT | Main Point of Contact(s): TL, DL, C | Status |
| 1 | United States of America | -10..-4 | Brian Christopher Dean (TL), no DL | Completed (4) |
| 2 | El Salvador | -6 | Humberto Alfonso Sermeño Villalta (TL), José Rodrigo Santamaría Castro (DL) | Completed (4) |
| 3 | Colombia | -5 | Mario Cruz (TL), Roger Trujillo (DL) | Completed (4) |
| 4 | Ecuador | -5 | Omar Nicolás Paladines (Invited Observer) | Completed (0) |
| 5 | Mexico | -5 | Marcel Stöckli Contreras (TL), Sebastian Sánchez Lara (DL) | Completed (4) |
| 6 | Peru | -5 | Raul Gallegos (Invited Observer) | Completed (0) |
| 7 | Bolivia | -4 | Willmar Alex Pimentel Sossa (TL), Jhonatan Castro (DL) | Completed (4) |
| 8 | Canada | -4 | Troy Vasiga (TL), John-Paul Pretti (DL) | Completed (4) |
| 9 | Chile | -4 | Catherine Espinoza (TL), Javier Marinkovic (DL) | Completed (4) |
| 10 | Cuba | -4 | Leonardo Cardona Luque (TL), Francisco Hernádez González (DL) | Completed (4) |
| 11 | Dominican Republic | -4 | Roberto Carlos Abreu Diaz (TL), Pedro Manuel Taveras Nuñez (DL) | Completed (4) |
| 12 | Venezuela | -4 | Emilio Nazareth Tirado Oviedo (TL), Jose Trinidad Trino Gomez Barreto (DL) | Completed (4) |
| 13 | Argentina | -3 | Mariano Maluf (TL), Agustín Gutiérrez (DL) | Completed (4) |
| 14 | Brazil | -3 | Ricardo Anido (TL), André Amaral de Sousa (DL) | Completed (4) |
| 15 | Iceland | 0 | Bjarki Ágúst Guðmundsson (TL), Bernhard Linn Hilmarsson (DL) | Completed (4) |
| 16 | Ireland | 1 | Stefan-Bogdan Marcu (TL), Colm Ó hIcí (DL) | Completed (4) |
| 17 | Morocco | 1 | Anas Abou El Kalam (TL), Moncef M'hasni (DL) | Completed (4) |
| 18 | Nigeria | 1 | Oluchi Jennie Bamidele (TL), Sarah Nkemdilim Arih (DL) | Completed (4) |
| 19 | Portugal | 1 | Pedro Ribeiro (TL), Pedro Paredes (DL) | Completed (4) |
| 20 | Spain | 1 | Jacobo Vilella Vilahur (TL), Joan Alemany Flos (DL) | Completed (4) |
| 21 | Tunisia | 1 | Dorsaf Benna (TL), Hichem Razgallah (DL) | Completed (4) |
| 22 | United Kingdom | 1 | Richard Forster (TL), David Mestel (DL) | Completed (4) |
| 23 | Austria | 2 | Helmut Achleitner (TL), Johann Fellner (DL) | Completed (4) |
| 24 | Belgium | 2 | Damien Leroy (TL), Bruno Ploumhans (DL) | Completed (4) |
| 25 | Bosnia and Herzegovina | 2 | Haris Gavranovic (TL), Adnan Šalaka (DL) | Completed (4) |
| 26 | Croatia | 2 | Krešimir Malnar (TL), Ivan Paljak (DL) | Completed (4) |
| 27 | Czech Republic | 2 | Zdeněk Dvořák (TL), Pavel Töpfer (DL), Martin Mareš (ITC) | Completed (4) |
| 28 | Denmark | 2 | Knud Fjeldsted (TL), Anders Roy Christensen (DL) | Completed (4) |
| 29 | Egypt | 2 | Haytham Farouk (TL), Mahmoud Badawy (DL), Eslam Wageed (IC) | Completed (4) |
| 30 | France | 2 | Mathias Hiron (TL), Simon Mauras (DL) | Completed (4) |
| 31 | Germany | 2 | Wolfgang Pohl (TL), Philip Lukert (DL) | Completed (4) |
| 32 | Hungary | 2 | Gyula Horváth (TL), László Nikházy (DL), Agnes Erdosne Nemeth (IC), Zsolt Németh (ISC), László Nyúl (ITC) | Completed (4) |
| 33 | Italy | 2 | Giorgio Audrito (TL), Edoardo Morassutto (DL), William di Luigi (ITC) | Completed (4) |
| 34 | Luxembourg | 2 | Gilles Englebert (TL), Luca Courte (DL) | Completed (4) |
| 35 | Macedonia | 2 | Emil Stankov (TL), Martin Dinev (DL), Mile Jovanov (IC) | Completed (4) |
| 36 | Montenegro | 2 | Goran Sukovic (TL), Ranko Cabrilo (DL) | Completed (4) |
| 37 | Netherlands | 2 | Eljakim Schrijvers (TL+IC), Jelmer Sybren Firet (DL) | Completed (4) |
| 38 | Norway | 2 | David Narum (TL), Birk Tjelmeland (DL) | Completed (4) |
| 39 | Poland | 2 | Piotr Chrząstowski-Wachtel (TL), Tomasz Nowak (DL), Jakub Łącki (ISC) | Completed (4) |
| 40 | Serbia | 2 | Marko Savić (TL), Nikola Milosavljević (DL) | Completed (4) |
| 41 | Slovakia | 2 | Michal Forišek (TL), no DL | Completed (4) |
| 42 | Slovenia | 2 | Darko Pevec (TL), Žiga Željko (DL) | Completed (4) |
| 43 | South Africa | 2 | Tian Cilliers (TL), Mohammed Taariq Mowzer (DL) | Completed (4) |
| 44 | Sweden | 2 | Johan Sannemo (TL), Simon Lindholm (DL), Fredrik Niemelä (ITC) | Completed (4) |
| 45 | Switzerland | 2 | Johannes Kapfhammer (TL), Timon Gehr (DL) | Completed (4) |
| 46 | Belarus | 3 | Alexander Buslavsky (TL), Kanstantsin Vilcheuski (DL) | Completed (4) |
| 47 | Bulgaria | 3 | Emil Kelevedjiev (TL), Iliyan Yordanov (DL) | Completed (4) |
| 48 | Cyprus | 3 | Panayiotis Eracleous (TL), Andronikos Charalampous (DL) | Completed (4) |
| 49 | Estonia | 3 | Sandra Schumann (TL), Targo Tennisberg (DL) | Completed (4) |
| 50 | Finland | 3 | Heikki Hyyrö (TL), Antti Röyskö (DL) | Completed (4) |
| 51 | Greece | 3 | Michael Chatzopoulos (TL), Nikolaos Papaspyrou (DL) | Completed (4) |
| 52 | Israel | 3 | Ron Ryvchin (TL), Omer Ronen (DL) | Completed (4) |
| 53 | Jordan | 3 | Mowaffaq Hanandeh (TL), Ashraf Ahmad (DL) | Completed (4) |
| 54 | Latvia | 3 | Mārtiņš Opmanis (TL), Andrejs Vihrovs (DL), Eduard Kalinicenko (IC) | Completed (4) |
| 55 | Lithuania | 3 | Jūratė Skūpienė (TL), Justas Klimas (DL), Valentina Dagiene (IC) | Completed (4) |
| 56 | Moldova | 3 | Sergiu Corlat (TL), Igor Bercu (DL) | Completed (4) |
| 57 | Palestine | 3 | Musa Alrefaya (TL), Samed Alhajajla (DL) | Completed (4) |
| 58 | Romania | 3 | Adrian Panaete (TL), George Chichirim (DL) | Completed (4) |
| 59 | Russia | 3 | Andrew Stankevich (TL), Alexey Maleev (DL) | Completed (4) |
| 60 | Saudi Arabia | 3 | Sultan Albarakati (TL), Esraa Almajhad (DL) | Completed (4) |
| 61 | Syria | 3 | Ubai Sandouk (TL), Hasan Jaddouh (DL) | Completed (4) |
| 62 | Turkey | 3 | Tolga Can (TL), Ahmet Soran (DL) | Completed (4) |
| 63 | Ukraine | 3 | Vitalii Bondarenko (TL), Andrii Pankov (DL) | Completed (4) |
| 64 | Armenia | 4 | Armen Andreasyan (TL), Levon Muradyan (DL) | Completed (4) |
| 65 | Azerbaijan | 4 | Rashad Mammadov (TL), Ibrahim Taghizade (DL), Araz Yusubov (IC) | Completed (4) |
| 66 | Georgia | 4 | George Mandaria (TL), Zaza Gamezardashvili (DL) | Completed (4) |
| 67 | Iran | 4.5 | Hamid Zarrabi-Zadeh (TL), Keivan Rezaei (DL) | Completed (4) |
| 68 | Kazakhstan | 5 | Temirlan Satylkhanov (TL), Aidos Nurmash (DL) | Completed (4) |
| 69 | Tajikistan | 5 | Alexandr Ismatov (TL), Akram Azamov (DL) | Completed (4) |
| 70 | Turkmenistan | 5 | Kochek Arazov (TL), Amangeldi Meretglychov (DL) | Completed (4) |
| 71 | Uzbekistan | 5 | Bahodir Gulmatov (TL), Asadillo Ganiev (DL) | Completed (4) |
| 72 | India | 5.5 | Madhavan Mukund (TL), Narayan Kumar Krishnan (DL) | Completed (4) |
| 73 | Sri Lanka | 5.5 | Adithya Narasinghe (TL), Suvin Kodituwakku (DL) | Completed (4) |
| 74 | Bangladesh | 6 | Mohammad Sohel Rahman (TL), Mohammad Kaykobad (DL) | Completed (4) |
| 75 | Kyrgyzstan | 6 | Pavel Pankov (TL), Kylychbek Uraiymov (DL) | Completed (4) |
| 76 | Indonesia | 7 | Felix Jingga (TL), Yehezkiel Raymundo Theodoroes (DL), Yugo Kartono Isal (IC), Jonathan Irvin Gunawan (ISC), Ashar Fuadi (ITC) | Completed (4) |
| 77 | Thailand | 7 | Nattee Niparnan (TL), Jittat Fakcharoenphol (DL) | Completed (4) |
| 78 | Vietnam | 7 | Thuan Do Phan (TL), Dong Do Duc (DL) | Completed (4) |
| 79 | China | 8 | Wentao Han (TL), Xin Zhao (DL) | Completed (4) |
| 80 | Hong Kong | 8 | Wing-ki Ngan (TL), Hau Chung Oa Yang (DL) | Completed (4) |
| 81 | Macau | 8 | Teng Lam (TL), Kuo Meng Sun (DL) | Completed (4) |
| 82 | Malaysia | 8 | Tan Wei Xin (TL), Tan Li Xuan (DL) | Completed (4) |
| 83 | Mongolia | 8 | Tsedevsuren Danzan (TL), Khuder Altangerel (DL) | Completed (4) |
| 84 | Philippines | 8 | Vernon Gutierrez (TL), Marte Raphael Soliza (DL) | Completed (4) |
| 85 | Singapore | 8 | Suhendry Effendy (TL), Aaron Tan Tuck Choy (DL), Tan Sun Teck (IC), Steven Halim (IC), Gan Wei Liang (ISC), Ranald Lam Yun Shao (ITC) | Completed (8) |
| 86 | Taiwan | 8 | Hung-Lung Wang (TL), Tsai Shi-Chun (DL), Greg Lee (IC) | Completed (4) |
| 87 | Japan | 9 | Hirotaka Yoneda (TL), Tomohito Hoshii (DL) | Completed (4) |
| 88 | Republic of Korea | 9 | Sung-Ryul Kim (TL), Inbok Lee (DL) | Completed (4) |
| 89 | Australia | 8..10 | Kevin Tran (TL), Angus Ritossa (DL), Benjamin Burton (IC) | Completed (4) |
| 90 | New Zealand | 12 | Margot Phillipps (TL), Ross Atkins (DL) | Completed (4) |
