As with the military's "don't ask, don't tell" policy, which was discontinued in 2011, the Boy Scouts ban was motivated in part by concerns about sexual contact among members.
The ban also appeased the religious and socially conservative organizations that sponsor many troops. A survey circulated by the group's executive committee earlier this year found that 51 percent of major donors opposed repealing the ban.
Debate over the ban reached the U.S. Supreme Court, which ruled in the 2000 case, Boy Scouts of America v. Dale, that the organization has a right to banish undesired members.
In addition to its ban on gay scouts, the group also bans atheists, regardless of age. A 2008 statement on the Boy Scouts national council's website explains that ban.
"Boy Scouts of America believes that no member can grow into the best kind of citizen without recognizing an obligation to God," says the statement. "Because of Scouting's methods and beliefs, Scouting does not accept atheists and agnostics as members or adult volunteer leaders."