Melbourne attracted more believers to a convention last year
More than 2,000 atheists from around the world are gathering in Melbourne, Australia, to celebrate their lack of religious belief.
It is thought to be the world's largest gathering of atheist thinkers.
They plan to issue a statement on what they say are the negative effects of religion on society.
All 2,500 tickets were sold out earlier this year, but a religious gathering at the same venue in December attracted three times as many delegates.
The Global Atheist Convention is bringing together scientists, philosophers, writers and comedians, says the BBC's religious affairs correspondent Christopher Landau.
They will be joined by bestselling author Richard Dawkins and discuss Islam and terrorism in a session titled The Cost of Delusion.
They will also hear a film proposal, exposing the amount taxpayers spend subsidising religion.
There is a determination to avoid what one session calls Atheistic Fundamentalism, says our correspondent.
Participants will be urged to avoid "missionary zeal" in their determination to promote their non-religious message to the world.