Figures from the literary world, showbusiness and politics are descending on Powys for the 2010 Hay Festival.
Among the headline speakers this year will be Deputy Prime Minister Nick Clegg, who will discuss the new coalition UK government.
Former Pakistani President Pervez Musharraf will also address the festival.
Running until 6 June, the festival is expected to attract 100,000 people.
It was confirmed on Wednesday, the eve of the festival, that Mr Clegg will discuss the new coalition government, the rule of law and constitutional reform with Philippe Sands on the festival's final day.
Hay Festival founder Peter Florence told BBC Wales it was a "coup" to be holding Mr Clegg's first public session, confirmed this week, since his appointment.
He said Mr Clegg would talk about the UK government coalition, the Chilcott inquiry into the Iraq war and reforming the constitution.
"He's very much aware that he's coming into an area where there was an incredibly rancorous Conservative-Liberal split and competition in [the constituency of) Brecon and Radnor[shire], also, actually, interestingly, in South Herefordshire, our neighbouring constituency.
"He is very keen to come and address some of the concerns that Liberals have about what happened."
Other political highlights include former Pakistan leader Pervez Musharraf, who stood down in 2008, and who will talk about the future of his country.
The president of the Maldives, Mohammed Nasheed, will talk to the former UK Energy and Climate Change Secretary Ed Miliband, about climate change and building democracy in a Muslim nation.
From the literary world, playwright Tom Stoppard will be appearing, as well as writers Martin Amis, Zadie Smith and 2009 Man Booker Prize winner Hilary Mantel.
This year will also see the launch of a search for the most beautiful tweet ever tweeted.
It will be judged by comedian Stephen Fry, and entrants can submit their own tweets - messages no longer than 140 characters - or nominate other tweeters.
On Wednesday, the site was opened especially for primary school children.
The first official day, Thursday, is devoted to secondary school children from Powys and Herefordshire as part of Hay's inaugural Schools Day.
Previous guests at the festival - now in its 23rd year - include Archbishop Desmond Tutu in 2009, former Beatle Sir Paul McCartney and former US presidents Bill Clinton and Jimmy Carter.