The sixth Harry Potter book has been published around the world, ending the wait for eager readers.
Fans queued at bookshops for Harry Potter and the Half-Blood Prince's release at 0001 BST on 16 July.
Author JK Rowling was at Edinburgh Castle where she read to 70 young fans who won the chance to be at the launch and interview her.
Ten million copies were expected to be sold worldwide within 24 hours, including two million in the UK.
"I'm excited about this book," Rowling said as she arrived at the castle.
"You get a lot of answers in this book. I can't wait for everyone to read it."
The young competition winners were led into the castle, which has been transformed into the entrance hall of Hogwarts School of Witchcraft and Wizardry for the event.
As the book was launched, Rowling appeared from behind a secret panel in the wall - shrouded by smoke - to read to them.
She told reporters that it meant "everything" to be in her home city for the launch.
"I left my daughter behind with a copy of the book. It is the first time she has had her hands on it," Rowling said.
"When I left she was laughing at something, which was quite encouraging, you can imagine."
The book has gone on sale in 15 countries - including the UK, US, Brazil and the Philippines - with many bookshops holding late night openings and Potter parties.
Book retailer Waterstone's opened 140 of its stores at midnight and online retailer Amazon received more than 400,000 advance orders in the UK alone.
A total of 550,000 copies of the book were sent around the UK by Royal Mail on Saturday, employing an extra 150 vans to deliver on time.
Britain's WH Smith chain said Harry Potter and the Half-Blood Prince sold at a rate of 13 copies per second overnight.
It said this broke the record set by previous instalment Harry Potter and the Order of the Phoenix, which sold eight copies per second when published in 2003.
Matthew Perren, manager of bookseller Ottaker's main Edinburgh branch, said about 50% of copies sold were the adult version of the book - featuring the same content but with a more "grown-up" cover design.
Harry Potter and the Half-Blood Prince was the first novel to be published simultaneously in Braille, large-print and standard versions in the UK.
Blind readers often have to wait months or years for new books to be converted into Braille.
Hundreds of Potter fans queued for hours outside the Waterstone's store in London's Oxford Street on Friday, many dressed as witches and wizards.
Savannah Mazda, 15, was first in the queue at Waterstone's in London's Oxford Street
At Mount Prospect, Illinois, more than 10,000 fans participated in a range of Potter-related activities, while in New York, the world's biggest toy shop - Toys R Us in Times Square - was transformed into the Hogwarts Academy.
Other countries, including India, Australia and New Zealand also held thousands of events to coincide with the launch.
The first five Harry Potter books have sold more than 265 million copies in 200 countries and have been translated into 62 languages.
But the run-up to the new book's release - the penultimate in the series - was not problem-free.
A store in Edinburgh apologised after putting the latest Harry Potter book on shelves early, allowing customers to read copies.
Israeli bookstore have been heavily promoting the book
Newsround Online reporters were able to read key parts of the book when it went briefly on display in HMV.
The store said it was an honest mistake and took the book off display as soon as it realised its error. No-one was allowed to buy the copies.
One boy in the US, Sylum Mastropaolo, was sold a copy of the book by mistake on Monday, but he and his parents returned it to the shop.
A court order was issued in Canada banning the disclosure of the story's contents after a number of the books were sold by mistake.