The rare gathering of security and intelligence officials from more than 50 countries in the birthplace of Usama bin Ladin sends a message of support for Saudi Arabia, which is battling a 21-month wave of violence by Bin Ladin's supporters.
The four-day conference will be held amid tight security at a hotel close to Saudi Arabia's interior ministry, the nerve centre of security services that was bombed on 29 December.
Saudi officials say the meeting, which also brings together UN and Interpol anti-terror experts, is more than symbolic.
Participants will pool experience in tackling terror, its causes and its links to organised crime, and propose practical joint steps to curb violence, organisers say.
President George Bush's Homeland Security Adviser Frances Townsend will attend, as well as treasury and state department counter-terror officials.
"I believe it will demonstrate, once again, that the United States and Saudi Arabia are engaging seriously to identify practical ways to fight terrorism, along with other nations," US ambassador to Saudi Arabia James Oberwetter said.
The Saudi Arabian army is battling
a wave of insurgency
But other diplomats doubt the United States and its Western allies will share much more than platitudes with conference delegates from Sudan, Syria or Iran, which Bush called the "world's primary state sponsor of terror" on Wednesday.
"We're a bit sceptical it will produce results from the intelligence point of view," said a security source from a European country that is sending delegates to the conference.
Stepped up campaign
Most of the hijackers behind the 11 September attacks in the United States were Saudis, and the kingdom was criticised for dragging its feet in the battle against al-Qaida.
But diplomats said it stepped up its efforts after triple bombings at expatriate residential compounds in Riyadh killed 35 people, mainly foreigners, in May 2003.
Wrecked houses in the al-Muhaya
compound, November 2003
Al-Qaida supporters, who aim to expel Westerners from the cradle of Islam and topple the pro-Western Saudi monarchy, have since taken captives and bombed government security targets, the US consulate in Jedda, a petrochemical complex and two other Western compounds.
Security forces say they have killed or arrested most of the network's top leaders, but analysts say the movement will remain a threat in the world's biggest oil exporter for years.