Greenbelt has been staged annually since 1973
Traditional Anglicans have criticised the UK's major Christian arts festival for inviting a gay American Bishop to speak.
Among those addressing the Greenbelt festival this year is the Bishop of New Hampshire, Gene Robinson, a gay man whose ordination by the Episcopalian Church was greeted with both outrage and celebration in various parts of the worldwide Anglican Communion.
Many people did not welcome his elevation, and the issue of gay clergy has become so contentious that it threatens to divide global Anglicans - some say it has already begun.
Last month, the Episcopal Church voted to end a three-year moratorium on electing gay Bishops, a move which may ultimately push the US Church out of the Communion.
This begs the question, why did Greenbelt's organisers invite one of the most controversial figures in the Church to speak, a decision which was bound to draw criticism from some sections?
Festival coordinator Beki Bateson, says the invitation was made solely on the strength of Bishop Robinson's earlier speaking appearances at other venues, and that his is just one voice amongst many.
"Sometimes those voices are not always programmed at the same festival and some issues including the debate around sexuality have been addressed over a number of years from varying perspectives."
Conservative Anglicans have remained unimpressed, reacting with dismay to Bishop Robinson's appearance.
They have accused the festival - which was once regarded as counter-cultural - of becoming conformist in its apparent wish to acknowledge modern diversity.
Canon Chris Sugden, a member of Anglican Mainstream, a pressure group campaigning for traditional biblical teaching on homosexuality, is unhappy with Bishop Robinson's invitation.
He acknowledges Greenbelt as a forum for exploring new ideas, but is concerned that no opposing viewpoint on human sexuality will be aired.
"Gene Robinson was invited because he's a controversial celebrity. So I suggest it's a sign of prejudice by Greenbelt that they haven't invited other speakers.
"The festival will be full of families with teenage children, a ready audience who might be persuaded by his [Robinson's] sophisticated presentation technique."
Speakers Canon Sugden would like to hear include organisations who say they can either change same-sex attraction, or enable gay men and women to remain happily celibate.
Dr Lisa Nollard is a historian who plans to be among the festival-goers over the weekend.
She has also criticised what she sees as the organisers' reluctance to allow an even-handed presentation of controversial topics.
"What discussions would I like to see? How about a workshop entitled 'Why a lot of women think abortion is a bad idea!'"
But many people either find those issues too controversial, she says, or they do not think they are deserving of "airtime".
Dr Nollard is looking forward to hearing Gene Robinson, and may well challenge him on his opinions.
"I've read a lot of what Bishop Robinson has written, and I've shaken my head."
As well as discussions, there is also music at Greenbelt
Changing Attitude, a leading pro-gay Church movement, will be laying out their ideas at the festival.
Its director, the Rev Colin Coward, says he is happy to have a debate on homosexuality, but that it is not appropriate to invite the "Ex-Gay" movement.
"There's a lot of evidence that trying to make somebody ex-gay doesn't work" he says.
"It's abusive. And those organisations are on the fringe, whereas Gene Robinson is an elected bishop."
For her part, Beki Bateson is adamant that all sides of the gay debate have been aired at Greenbelt over the years, and she rejects the accusation that teenagers will leave Cheltenham racecourse with only one spiritual view of sexuality.
"Greenbelt believes that young people learn what they want to learn," she adds.