Olympiad Archive
Here is a list of links to High School and College National Olympiads and Competitions on Science (mainly Mathematics) all over the world, in different languages. A good number of websites mentioned in this section are taken from the Countries page in the website of International Mathematical Olympiad.
NOTE. This page is incomplete. If you want to add a link, either add it to the table or post it in this topic.
National Olympiads/Competitions
 Physics Cup
Country  Olympiad Description and Link  Subject  Language  

Argentina  Full Archive of Mathematical Olympiad Problems 
Mathematics 
Spanish  
Australia 

English  
Belarus 


 
Belgium 

Mathematics 
Dutch  
Britain 


English  
Canada 

English  
China 


English  
Czech Republic 



Estonia 
http://www.ioc.ee/~kalda/ipho/E_S.html (English,Estonian) 
(Geometry) 
 
Hong Kong 

Mathematics 
English, Cantonese  
India 


English  
Iran 
Mathematics 
 
Italy 

 
Israel 


 
Romania 


 
Russia 


 
Serbia 


 
Slovakia 


Slovak  
Spain 
Mathematics 
Spanish  
Switzerland 


 
Turkey 

Turkish  
USA 


English 
International Olympiads/Competitions
EnglishOlympiad Description and Link  Subject  Language 

APhO (Asian Physics Olympiad) 
Physics 
English 
BAUPC (Boston Area Undergraduate Physics Competition) 
Physics 
English 
EMIC (Elementary Mathematics International Competition) 
Mathematics 
English 
EuPhO (European Physics Olympiad)

Physics 
English 
ICHO (International Chemistry Olympiad)

Chemistry 
English 
IMO (International Mathematical Olympiad) 
Mathematics 
All languages 
IOI (International Olympiad in Informatics) 
Informatics 
All languages 
IPhO (International Physics Olympiad)

Physics 
English 
IPT (International Physicists' Tournament) 
Physics 
English 
ITMO/AITMO ([Asian] International Teenagers Mathematical Olympiad)

Mathematics 

IWYMIC (The International World Youth Mathematics Intercity Competition) 
Mathematics 
English 
IYPT (International Young Physicists' Tournament) 
Physics 

KöMaL Contest 

English 
NBPhO (Northern Baltic Physics Olympiad)

Physics 

Olimpiadas Iberoamericanas de Física 
Physics 
English 
Online Physics Brawl 
Physics 
English 
Princeton University Physics Competition 
Physics 
English 
Physics Cup 
Physics 
English 
Rudolf Ortvay International Competition in Physics 
Physics 
English 
The University Physics Competition 
Physics 
All languages 
References
 International Mathematical Olympiad (Official Website)