Qualification
Approximately 70 to 80 people qualify for and are invited to write the CMO each year. Students must not have written the Putnam Competition and must meet age, full-time school enrollment, and Canadian Citizenship (or permanent residency) requirements. Students do not have to be living in Canada, as long as they are Canadian citizens.
Participants are invited to write the CMO usually because of excellent results at the Canadian Open Mathematics Challenge (COMC). Approximately the top 50 students from the COMC earn invitations to the CMO. A Qualifying Repêchage (CMOQR) is offered as a "second chance" for the next highest 50 - 100 students from the COMC. About 20 students are chosen from the Repêchage and are then invited to the CMO.
Top students in certain other top Canadian competitions are also given invitations. The organizing committee may also invite participants based on their earlier CMO experience or their performance at APMO or USAMO competitions.
Read more about this topic: Canadian Mathematical Olympiad