Having tackled the secretive Catholic conservative group Opus Dei, Dan Brown says he's writing his next book about the Freemasons.
The Freemasons say they are simply a fraternity that aims to make good men better and to support each other. Because they are essentially secret, however, groups such as the Freemasons can stir all kinds of theories.
The all-seeing eye atop the pyramid on the $1 bill is a Masonic symbol. Some say that some of the great American buildings have Masonic symbols incorporated into their architecture.
Many of our Founding Fathers, including George Washington, Benjamin Franklin and John Hancock, were Freemasons. There are currently 1.7 million members, though membership has been declining since 1960.
Some conspiracy theorists say that the Freemasons, or Masons, have designs on government control.
"The thing people think about when they think of Masonry is secrecy. They think of this hidden order that they know almost nothing about," said Steven C. Bullock, author of "Revolutionary Brotherhood: Freemasonry and the Transformation of the American Social Order."