Fans around the world are finally getting their hands on the sixth Harry Potter book, Harry Potter and the Half-Blood Prince.
The plot of the new book has been kept firmly under wraps
The latest instalment of the adventures of the boy wizard, by author JK Rowling, went on sale at 0001 BST on Saturday.
BBC correspondents reported on the atmosphere in London, Edinburgh, Sydney, New York and Delhi, which were among those cities hosting launch parties.
2026 local time (1556 BST) Soutik Biswas, BBC News website, Delhi
A plush bookstore in downtown Delhi was the scene of the end-of-the-day Potter launch festivities.
Some 70 children wearing Potter costumes, tattoos and spectacles turned up at the store even as their parents stared on.
In the deafening din of excited children, a few flipped through the pages of the new book and made predictions on the fate of the dramatis personae.
The event was hailed as India's biggest book launch in recent years
The muzak was strangely Eagles and hip hop as the children played a Quidditch game with small brooms and colour balls, participated in a crossword contest and did a magic jig.
In the best tradition of India's intensely political capital city, an uneasy, inarticulate politician had been curiously invited to be master of the ceremonies.
"I am a stranger to the world of creative arts," he mumbled. "But I hope Rowling keeps writing these books."
For once, the children cheered a politician lustily. And television news was reporting that it had been the biggest launch a book - any book - India had seen in a long, long time. Potter power rules.
0140 local time (0640 BST) Matthew Davis, BBC News website, Union Square, New York
Pottermania is alive and well in New York, but queues for the latest instalment of the young wizard's adventures look set to go on for hours to come.
In bookstores around the city, copies of the Half-Blood Prince are said to be flying off the shelves faster than a hot-wired broomstick.
Shortly after midnight the floor of one leading bookshop was a sea of fans craning for a view of the freshly-opened boxes of books. In an effort to avoid a surge towards the tills, staff at Barnes and Noble had handed out more than 1,000 wristbands with numbered spots in the queue.
But the prospect of long waits did not dampen the ardour of those keen to discover the latest twists to the Potter saga at the earliest opportunity.
Potter fan Rachel Grandi is the first to buy the book in Union Square
The carnival atmosphere was stoked by Jim Dale - voice of the Potter audio books - who gave a series of entertaining readings.
As midnight arrived in store, a woman in an owl costume appeared onstage bearing a freshly-minted batch of books, whereupon Mr Dale read aloud the first words of the Half Blood Prince to rapturous applause.
Throughout the afternoon in Times Square, fans had camped out under the feet of tourists and beneath a huge countdown clock that helped build a sense of excitement and anticipation outside the world's largest toy store.
Camera crews were on hand to record the rush as the doors of the shop were thrown open, and staff were expecting to push on through until dawn at the tills.
1400 local time (0500 BST) Phil Mercer in Sydney, Australia
It's five hours since the new Harry Potter adventure went on sale and retailers in Australia are reporting a full-blooded day of business so far.
"It's been an unusually hectic day," said Christina Metlikovec, from the Dymocks bookshop in Bondi Junction in Sydney.
"People have been so wildly excited when they've come in," she added.
Bea Brabante started reading the book straight away in Sydney
Echoing the thoughts of politicians and parents, Mrs Metlikovec said that the Harry Potter phenomenon was not only good for business but for society too.
"It has encouraged kids who wouldn't normally pick up a book to
suddenly think 'What is this all about?'" she said.
"It's done wonders - absolute wonders - for kids' reading."
The Sydney Morning Herald is offering 50 free copies of Harry Potter and the Half-Blood Prince.
There is, however, a catch. Readers must first complete a giant Harry Potter crossword and then go into a prize draw.
For ardent Potter fans, the clues should be a breeze, among them "incantation spoken to defeat a Boggart", "fastest, most technologically-advanced broomstick" and "magical creature that's part horse, part eagle"?
0920 local time (0450 BST) Soutik Biswas, BBC News website, Delhi
Delhi's poky Midland Book shop opened its doors at 0430 on a cloudy, rainy morning as children, mostly accompanied by bleary-eyed parents, arrived to pick up the first copies of the new Harry Potter book.
A kiosk was set up outside Mr Baig's shop to cope with demand
Two years ago when the last Potter book came out, shop owner Afsar Baig opened his shop after eight in the morning.
"But this time the craze has reached such a peak that my clients demanded that I opened my shop around the time the book was released worldwide," he says.
He wasn't disappointed - within three hours of opening the shop nearly half of the 650 cash-paid advance copies had already been picked up.
And people were also streaming in to get a copy of the book.
To cope with the rush, Mr Baig put up a modestly-decorated kiosk outside his bookshop to sell the book.
"I am so excited. I am going to finish this one today," said Rajiv Dhawan, 13.
A woman walked into the store saying: "Now where is this book my children have been waiting for the last two years? Give it to me!"
Outside, the Potter launch was the top item on news television.
They were reporting queues outside Mumbai bookshops at the crack of dawn, with children togged out in Potter costumes and cutting Potter cakes outside Delhi stores.
There was talk of a bookstore in Chennai which has over 2,000 advance cash-paid orders.
Booksellers were saying that the nearly 150,000 copies of the first consignment of the new Potter book would be sold out within two weeks.
Rowling rules in former Raj country.
2045 local time (0145 BST) Matthew Davis, BBC News website, Union Square, New York
Midnight magic is the theme as New York builds up to the big launch, five hours behind the UK.
Entertainers were on hand in New York to keep waiting children occupied
Barnes and Noble's flagship bookstore in Union Square has been transformed into Hogwarts Castle for the evening with stilt-walkers, wandering magicians and fans dressed in uniforms giving each floor a flavour of the books.
Television crews are here in force, the cameras are on and punters young and old are in party mood.
More than 500 people cram in among the shelves to watch a hastily-edited broadcast of JK Rowling's speech at Edinburgh Castle.
The crowd - many wearing round plastic Potter specs are waiting for the voice of the audio books, Jim Dale, to lead the countdown to midnight with a reading from the Half-Blood Prince.
Everyone who wants to buy a copy has been given a wristband - yellow for pre-orders, orange for the rest. There are hundreds of yellows, and I am number 338 orange - it could be a long night.
0945 local time (0045 BST) Phil Mercer in Sydney, Australia
"It's better than Christmas morning!" enthused Jan, a mother of two, who braved the winter chill in Sydney to snare one of the first copies of Harry Potter and the Half-Blood Prince.
Around Australia queues snaked around bookshops well before the official launch.
At 9.01am the doors to the Dymocks store in Bondi Junction in suburban Sydney opened.
"I've been waiting for this for two years. I have big, big expectations!"
said Lucy Blackwell, a 17-year-old student.
There were loud cheers as the sixth instalment of JK Rowling's fantasy adventure finally went on sale.
John Watkins, a minister in the New South Wales State government, was on hand to do the official honours. He said that after the terrorist bombings in London, Harry Potter and the Half-Blood Prince would provide some light relief.
"At any time Harry Potter been a fantastic thing for kids and parents," Mr Watkins told the crowd.
"But when the dark news around the world is impacting on families, it's great to have a celebration of children's imagination, something that's good and positive."
0035 BST Newsround website's Neil Doughty in Edinburgh
At Waterstone's in Edinburgh there was a countdown ahead of the opening and even half an hour after the book went on sale there were still huge queues outside.
It really built up within the past hour and there are still a couple of hundred people queuing.
Everyone seems really excited about finally getting their hands on the book.
There are camera crews everywhere.
One lucky nine-year-old girl who had won a competition was chauffeured to the store in a limo and had the honour of opening a special trunk, signalling the book was officially on sale.
0030 BST Newsround website's Steve Goggin in Oxford Street, London
The atmosphere leading up to the launch was electric. There was a big countdown from 10 as Waterstone's prepared to open its doors, then there were sound effects of the Hogwart's Express.
Streams of people have been coming into the shop and joining the orderly queue. They pick up their book go to the cash desk, where there are loads of staff.
After they have paid, each gets their book stamped with the words: "I was one of the first people to buy the book."
2325 BST Newsround website's Steve Goggin in Oxford Street, London
The atmosphere outside Waterstone's has gone crazy, fans are completely blocking the pavement outside the shop as they wait to go in.
There are people doing the "Mexican wave" up and down the queue and buses and cars are beeping their horns as they go past, which makes everyone scream. There is just so much noise.
As well as fans there are also lots of media people, filming and interviewing those in the line.
The shop has now closed to normal customers and there is a big red curtain up over the window and a giant book cover over the door.
The queue now goes all the way down New Bond Street, which is quite a way from the actual shop. They won't be experiencing quite the atmosphere all the way back there but some have brought their deckchairs and flasks for the wait.
Waterstone's expects to stay open until at least 0300 to satisfy demand for Harry Potter and the Half-Blood Prince.
2100 BST Newsround website's Neil Doughty in Edinburgh
We have been walking around the bookshops of Edinburgh to gauge the appetite for the new Harry Potter in the build up to the launch.
So far it is much lower key than in London, with only a few people queuing outside shops.
We bumped into some little girls dressed up as Harrys and Hermiones on their way to the castle for the launch.
We have also seen the horses being groomed and carriages being prepared for the launch which will take the competition winners to Edinburgh castle.
Ottakar's bookstore is holding a party for about 100 children, inviting them into the shop for a few hours before the book goes on sale.
2025 BST Newsround's Steve Goggin and Rebecca Lumb in Oxford Street, London
One group of teenage girls has been queuing outside Waterstone's since 0630. The very first person in the queue was at the head of the line for the release of the last book.
Waterstone's says there are a lot more people queuing this year than last time. There is lots of entertainment laid on to keep everyone happy, and staff handing out drinks because it has been so hot.
There is a really fun atmosphere for the kids. Some of them have even said they are having such a good time they are not in such a hurry to get their hands on the book.
There are lots of people dressed up as Harry Potter or Hogwart's witches and wizards.
The shop has got barriers up keeping everyone in line - it is still open to normal customers - and the queues are snaking around the streets.
There are people walking up and down dressed as characters from the book, including a great Moaning Myrtle moaning about having to queue.