An exhausting eight days lie ahead. More than 20,000 people are expected to attend the 140 events. Lord (Roy) Jenkins is due to discuss his biography of Gladstone, the former Archbishop of Canterbury, Dr Robert Runcie, runs a ecclesiastical eye over the works of Thomas Traherne, a 17th-century poet who exposed the falsifying of church documents in Rome, Ted Dexter bats on about cricket and Courtney Pine will set out to prove that jazz is more than blues and boogie.
The town claims to house the world's largest collection of second-hand books - more than 2 million, according to Richard Booth, who pioneered the idea 25 years ago and later crowned himself "King of Hay".
He describes the festival as a gathering of literary groupies. "Hay lives all year round - not just at festival time, when people travel long distances and pay to hear writers and 'personalities' talk about each other in a big tent."
Away from the festival, held under canvas in the grounds of a school, books covering everything from archaeology to zoos, taking in all strands of literature on the way, are spread among 40 shops.
One of the most esoteric among the 20,000 titles in Mark Westwood's shop is the 220-page Function and Form of the Sloth, by M Goffart, assistant professor of physiology at Liege University. A snip at pounds 10 for students of the indolent arboreal creature.
One collection of much interest, but definitely not for sale, is the Pinocchio library displayed at a restaurant named after the long-nosed puppet. It even includes a Pinocchio volume translated into Japanese.
Hay also boasts a shop selling only Teddy Bears and a retailer called Mr Puzzle's Jigsaw World. All of which may provide diversions for festival- goers.
Sponsors include local solicitors Gabb & Company and the Brook Street Pottery, as well as national names like Marks & Spencer and Carlton Television.
Earlier this week, television teams from France, Germany and Venezuela were roaming the little town, which is dominated by the 13th-century castle where Mr Booth reigns. Carol Diaz from Caracas asked breathlessly: " How do you manage to keep this little city so beautiful?" No clues were found in the Federal Bank of Chicago's Milwaukee Economy (price pounds 2) that she was studying at one of the "honesty bookshops" - outdoor emporiums where buyers are trusted to put cash in a hole in the wall.
Hay is shot through with the quirky and unorthodox. The festival's president, the Welsh nationalist peer, Lord Elis-Thomas, an avowed Marxist in his previous incarnation as Dafydd Thomas MP, holds a doctorate for his thesis on Welsh medieval poetry. No doubt a copy of that work lurks somewhere in Hay's bibliographical labyrinths.
The festival director, Peter Florence, points out: "The familiar Hay preoccupations with sex, politics, gardening and history are all well represented." Enter: stage slightly right, the member for South Derbyshire.