Mathematical circles are gatherings that give mathematicians the opportunity to share their deep understanding and appreciation for the subject with school students who are looking for new challenges in mathematics. While solving problems is emphasized, the circles contain considerable amounts of mathematical ideas and techniques that will be broadly helpful. The books in the series come from several sources: translations of suitable books from Russian or Eastern European sources, books written in English for this audience, a small number of practical books for organizers of mathematical circles. The books are suitable for leaders and participants in mathematical circles. Parents of the participants will also find the books quite useful. The series is copublished by the Mathematical Sciences Research Institute and the American Mathematical Society. (ISSN 1944-8074) (LC 2008030521) Softcover.