BBC: BBC Middle East analyst Roger Hardy has spent the last two months investigating Wahhabism, Saudi Arabia's austere brand of Islam.
In the first of a two-part series, to be broadcast on the BBC World Service, he looks at the fierce debate over whether Wahhabism and Saudi petrodollars have fomented extremism.
"The essence of Wahhabism is purity," says Lawrence Wright, author of a Pulitzer-prize-winning book about al-Qaeda.
"They are only interested in purification - and that's what makes them so repressive."
Prince Turki al-Faisal, the former head of Saudi intelligence and former ambassador in London and Washington, dismisses the accusation out of hand.
"From our point of view in the kingdom, there is no such thing as Wahhabism. That's a canard."
Saudis have never cared for the "Wahhabi" label which historically was a term of abuse applied to them by their critics.
They are highly sensitive to the charge that they have used their vast oil wealth to turn an obscure desert sect into a global force. Jihad and the Saudi petrodollar (more) By Roger Hardy
Mark Alexander
