Sir Elton John, Kylie Minogue and Sir Paul McCartney are among the stars getting ready to perform for the Queen as she celebrates her Diamond Jubilee.
The musicians will play on a specially-constructed £200,000 stage built around the Queen Victoria Memorial outside Buckingham Palace in London.
The show starts at 19:30 BST and will be broadcast on BBC One.
It closes three hours later as the Queen lights the National Beacon, the last of 4,500 beacons around the world.
The Duke of Edinburgh will not attend after being taken to hospital with a bladder infection.
Acts including Stevie Wonder and Jools Holland have been running through sound checks ahead of the event.
Other artists taking part in the show include Jessie J, JLS, Robbie Williams, Dame Shirley Bassey, Ed Sheeran and Sir Cliff Richard.
"This is the only time in our lives we're going to be involved in something like this," said JLS member Aston Merrygold.
Sir Tom Jones, who first performed for the Queen at the 1967 Royal Command Performance, said he was looking forward to appearing before her again.
"It does make you feel different," he told the BBC. "It keeps you on your toes."
Classical music will be represented by the BBC Concert Orchestra, Bryn Terfel and pianist Lang Lang.
"I always wanted to play at Buckingham Palace and this is actually the first time," Lang Lang told the BBC, saying he would "need to keep his fingers warm" in order to perform.
"It just feels really English and pleasant... apart from the fact it's just started to rain," said singer Cheryl Cole.
The Girls Aloud star will perform a duet with Take That's Gary Barlow, organiser of Monday's concert.
"I've known Gary for years and years and we've always wanted to do something," said the 28-year-old.
Between the music, hosting duties will be handled by Rob Brydon, Miranda Hart, Lenny Henry and Lee Mack.
"It's going to be a great atmosphere," Henry told the BBC. "It's an honour to be asked.
"I was whizzed up onto the stage and Paul McCartney was singing Live And Let Die. I was just blown away."
More than 10,000 people won tickets to the show in a public ballot and attended a Jubilee picnic in the Buckingham Palace Garden ahead of the event.
Thousands more will watch the concert on big screens set up in Hyde Park, St James's Park and on The Mall.
The show is a joint venture between the BBC and Barlow, who co-wrote Sing, the official song for the Queen's Diamond Jubilee celebrations.
More than 200 people will take to the stage to perform the track later.
"The Royal household just wants the public to have a great time," Barlow told ITV earlier.
"We tried to pick artists from right across [the Queen's] reign - from the '50s and '60s right up to the modern day."
The concert will include classic hits and one-off collaborations, and the stage has been designed by world-renowned architect Mark Fisher, who has worked for U2, Robbie Williams and The Rolling Stones.
Pop veterans Madness will perform Our House from the roof of Buckingham Palace - during the Golden Jubilee concert in 2002 Queen guitarist Brian May played the National Anthem there.
As well as BBC One, the concert will be broadcast live on BBC One HD and BBC Radio 2 in the UK, and to millions around the world.
US viewers will be able to watch highlights on ABC on Tuesday.
Source BBC News