The Order of the Arrow is one of the only organizations in the world where members are elected by non-members. The only way for a Scout to become a member of the Order of the Arrow is to be elected for this honor by his fellow Scouts.
To be eligible for election a Scout must hold the First Class rank and have camped 15 days and night with his Troop. Troops hold Unit Elections between February and May, and they are facilitated by representatives from the local Chapter. Scouts who have been elected by their Troop are then recognized and Tapped Out at a special Wednesday night at Summer Camp.
After being elected the Scout must complete the Ordeal, which is a series of tests of his sincere dedication to the high ideals of Scouting and Order. If he is faithful in performing the tests, he takes a solemn pledge of service and is admitted into the Order.
If you are interested in becoming a member of the OA and meet the requirements talk to your Scoutmaster about when your Troop is holding unit elections.