By Ian Youngs
Music reporter, BBC News
Jay-Z's booking caused controversy in 2008 - but he won over doubters
A year ago, rap star Jay-Z and US band Kings of Leon blew away critics at the Glastonbury Festival. This weekend, it's the turn of ageing rockers Bruce Springsteen and Neil Young to top the bill.
Organisers Michael and Emily Eavis say booking headliners comes down to a mixture of instinct and chaos - and who will play on the cheap.
This time last year, the Glastonbury Festival looked like it might be in trouble.
It was the first time for 15 years that tickets had not sold out in advance, with murmurs of discontent aimed at the choice of headliners.
Would a US hip-hop star really work at a British rock festival, and were Kings of Leon really headline material?
As it turned out, he did, and they were.
"We had the last laugh last year, didn't we?" Michael Eavis chuckles.
Michael and Emily Eavis say they judge bands on live sets, not record sales
As this year's extravaganza approaches, 39 years after the first festival, Michael is still the festival figurehead and still books the big bands, helped by his daughter and a small, trusted cabal.
So whose bright idea was it to book Jay-Z?
"You want me to tell you the truth about it?" asks Michael.
"The truth about it is that we thought Radiohead were going to do it. I was rather relying on Radiohead doing it."
When the band decided against it, opting to play their own summer shows instead, Michael phoned his daughter and told her: "We're stuck."
Emily, 29, made some calls, came up with the idea of Jay-Z and instructed her father to phone the US superstar's agent.
Michael may be one of the coolest 73-year-olds around - but some parts of pop culture have passed him by.
His daughter had to write "Jay-Zee" on a piece of paper to make sure Michael would pronounce the name correctly on the phone. "I had to get it right didn't I?" Michael says.
The agent tried to persuade him that Kanye West would be more suitable for a Glastonbury crowd, but Michael was unmoved. After a 45-minute phone call with Jay-Z's manager, the gig was on.
Kings of Leon worked their way up the bill at Glastonbury over five years
"Spot on. Absolutely 100% right, that was," the dairy farmer reflects. "That was the most significant thing we've ever done because we were crossing boundaries and going into new territory."
For Kings of Leon, who headlined the Friday night, Glastonbury was the launchpad for an ascent to the top of the charts and genuine stadium status.
Emily had been impressed as they had worked their way up the bill in previous years, and decided they were ready to make the step up.
"We just make a judgement on what we see and what we hear really," Michael says. "That was a good one. That could have gone wrong, but they were so good for us."
Did they even get an advance listen of the band's new album - released three months after the festival - to make sure the new material was any good?
"We didn't," Emily says. "The thing is, you don't need a good album. You need to be able to play a really good live set. We're not bothered about how many records you've sold."
Every year, around half a dozen acts - the biggest names on the circuit at the time - are in the frame to top the bill on the Pyramid Stage.
Michael and Emily's personal tastes count for a lot, and Emily puts much of it down to gut instinct. Michael says the choice of headliners is generally a "very chaotic procedure".
But there are also big financial constraints, meaning Glastonbury has to persuade stars to play for roughly 10% of the fee they would get elsewhere.
"The bottom line is that we take what's on offer, really," Michael says.
Glastonbury's spending power is spread thinly across all the whole festival, rather than concentrated on the headliners, Michael says.
"It's like Marmite. You can't give £1m or £2m for a headliner, it doesn't work like that, because we wouldn't have anything to spend on the fields further away."
They tempt stars by stressing the festival's legendary history and its charitable, political and environmental legacy - as well as the prospect of selling lots of albums, T-shirts and tickets to people who see the show on TV.
Referring to Springsteen's appearance on Saturday night, Emily adds: "It's so good that Bruce has done it, because he could have taken any number of huge offers, and he's chosen to do this."
When Michael first approached Springsteen's agent, the message was clear - you can't afford him.
So they put together a dossier for The Boss, packed with information about the festival, its good causes and ideology. It won him over.
The presence of two icons does not represent a deliberate move away from younger headliners, rock bands or British stars, the pair say.
"We do not think like that," Emily says. "We don't sit around a table with goggles working it all out.
"We had a chance of two amazing legends and there's no way we could turn one down just because we shouldn't have them the same year.
"And we're not going to turn them down because we're ageist. We couldn't fit any more new bands on than we do. But we have the kings at the top."
Do they ever consult market research?
"No," says Emily firmly. "Not interested," bellows Michael.
They could tell you who your audience is and...
"No! No!" Emily interrupts. "We know they're great. We don't need to know any market research. Market research is death to everything."
"No, we're not interested," Michael insists again. "No way."
Their instincts have been pretty good so far - and after last year, it would be foolish to doubt them now.