Eligibility
In order to be eligible to take the USAMO, a participant must be either a U.S. citizen or a legal resident of the United States or Canada. Only U.S. residents and citizens may join the American IMO team. In addition, all participants, regardless of geographic location, must meet qualification indices determined by previous rounds of the AMC contests. Entry to the USAMO is by invitation only.
Read more about this topic: United States Of America Mathematical Olympiad