A name-dropper's dream, the 11-day festival, which ended earlier this month, attracts heavyweights in storytelling, science, the environment, history, architecture, adventure, comedy and more.
This year featured the likes of V.S. Naipaul, Nigella Lawson, ex-Python Terry Jones, Rob Lowe, Paul Theroux, Julian Assange, the Hypnotic Brass Ensemble, comedian Jason Byrne and Bob Geldof.
Kiwis including Emily Perkins, Damien Wilkins and Catherine Chidgey have appeared in years past; this year expat opera singer Jonathan Lemalu performed in a local church.
It's a pop-up world of panama hats and outdoor reading (when it's sunny), scarves and cups of coffee (when it's not), and an erudite audience. The "Hay audience" seems to be a source of pride: it gets many a mention from speakers for its genteel nature, insightful questions and general lack of spleen-venting.
Vanessa Redgrave appeared to talk about her life and political work, and act in a play about American interrogations at Guantanamo Bay.
"What makes Vanessa Redgrave tick when she's appearing in a show on Broadway? What makes Vanessa Redgrave tick when she's doing Coriolanus with Ralph Fiennes?" asked the interviewer of his poised, gracious subject. "Ralph Fiennes makes me tick," she answered, smiling. There were no arguments.
Some authors had appeared at this year's successful Auckland Writers & Readers Festival. Palestinian doctor Izzeldin Abuelaish, who lost three daughters to Israeli shells in 2009, drew a standing ovation at Hay.
A.A. Gill sharpened his satirist's tongue when asked about his recent trip to Godzone. "New Zealand is properly weird: obsessed with rugby and coffee," he declared. His amusement at this "curious combination in the NZ Lonely Hearts column" was matched only by his glee in repeating an oft-heard phrase - "World famous in New Zealand".
From its beginnings as a 22-event gathering in 1988, Hay has grown to offer more than 600 events - and more than 225,000 tickets were sold this year. The not-for-profit institution has also expanded to Spain, Colombia, India, Lebanon, the Maldives and Mexico.
Director Peter Florence, likeable and well-connected, seems on a mission. Why the drive to go global? "To have a whole lot of fun," he says at first. Later, he expands. "The desire to explore other cultures and get beyond Britain's heroic isolationism.
"We're one of the world's most dynamically international countries, but we don't reach out ... as much as people with less dominant languages."
They bring punters through the door from an early age. Hay Fever, the excellent mini-festival for children and teens, attracts rock star-league guests: Judith Kerr, Philip Ardagh, Eoin Colfer. Jacqueline Wilson drew more than 1000.
The ebullient Michael Morpurgo, author of War Horse and a former Children's Laureate, admires New Zealand's child literacy work - and thinks Margaret Mahy is wonderful.
The festival is perfectly complemented by Hay town, with its pretty stone buildings and 30-odd second-hand bookshops. Locals stage art exhibitions and concerts, and while pubs inexplicably didn't stay open late to capitalise on the crowds, the iconic Richard Booth's Bookshop became a cocktail bar with music, dancing and alcohol-fuelled browsing.
I was enthralled by Rolf Heuer, the director-general of the Large Hadron Collider in Switzerland. He explained that such seemingly abstract goals could bear real fruit for humankind: for example, an offshoot discovery during the search for anti-matter is now used in hospitals.
"If we stop pushing back the frontiers of knowledge, at some stage we stop being human." That natural curiosity is what draws people to Hay - and why it's worth going.
* Mary de Ruyter is a NZ journalist travelling in Europe.