Database currently contains 20,945 math problems from 38 journals and 21 contests.

Collection of contest problems from New Zealand Math Olympiads and Auckland Mathematics Olympiad.

International Math Olympiad problems and solutions from 1959 to present, collected by John Scholes.

Solutions and Comments.

Contest questions from the 1998 Douglas Zare's internet contest.

Complete set of all International Mathematical Olympiad problems with solutions. Also includes problems sets from other national and international contests.

Sources of information about mathematical problem-solving. Focusing on long-answer type problems found on Olympiad-type contests or in problem sections of math journals.

Problems from UK Math Olympiads and a collection of training materials.

In particular, from Iran.

Collection of problem sets from International and National Mathematics Olympiads.

Old sample problems from Putnam training sessions, by Monica Nevens (University of Ottawa).

Jeffrey Lockshin's collection of mathematical problems, invented for mathematical olympiads all over the world.

Archive of problem sets and solutions from Wisconsin Mathematics, Engineering and Science Talent Search.

Mathematics problems for middle school and high school math competitions with topics range from algebra and geometry to probability and trigonometry.

Large archive of problems and solutions from Professor Kahan's Putnam Problems Practice Seminar.

Supplementary problems and related links by Byungchul Cha (Johns Hopkins University).

Three sets of practice problems in PDF format compiled Yang Wang of Georgia Institute of Technology.

Training resources include problems and partial solutions.

Practice problems for Putnam competition in postscript and PDF format. Page organized by Harry Tamvakis (Brandeis).

Contest problems and solutions for The International Mathematics Tournament of the Towns.

Problem sets from weekly practice sessions.

Problems for the US Mathematical Olympiad (1989-2003), International Mathematical Olympiad (1986-2003), Asian Pacific Mathematical Olympiad, and the Team Selection Test.

Problems without solutions.