Contests
Past problems from the competitions students actually sit, from the Philippine Mathematical Olympiad to the IMO.
Philippine contest papers are hard to come by online. The PMO, MTAP, Math Count PH and the competitions the universities run each have a long history, but their past problems are scattered across photocopied reviewers and old forum threads. This is an effort to gather them in one place.
Every problem is rated for difficulty from how solvers actually do on it, so you can start where you are and work up. Solve one and its discussion opens, with other solvers' approaches to compare against your own. Problems from the AMC, AIME and the international olympiads sit alongside them for anyone training beyond the national stage.
Philippine Contests
Past problems from the Philippine Mathematical Olympiad, MTAP, Math Count PH and the contests the universities host, rated for difficulty and open for discussion once you solve them.
Regional Contests
Competitions from across Asia and beyond.
American Contests
The AMC ladder, the AIME, HMMT and the other contests many olympiad students train on.
Mathematical Olympiad
Problems from the International Mathematical Olympiad and its shortlists.