Following are contestants of the 16th IOAA:

Armenia
Australia
Azerbaijan
Bangladesh
Brazil
Bulgaria
Canada
China
Colombia
Croatia
Cyprus
Czechia
Ecuador
Estonia
Georgia
Germany
Greece
Hungary
India
Indonesia
Iran
Italy
Japan
Kazakhstan
Kyrgyzstan
Latvia
Lithuania
Malaysia
Nepal
Netherlands
Norway
Pakistan
Paraguay
Philippines
Poland
Portugal
Qatar
Romania
Singapore
Slovakia
Slovenia
South Korea
Sri Lanka
Sweden
Thailand
Turkey
Ukraine
United Arab Emirates
United Kingdom
United States of America
Vietnam