Five million copies of the book were sold in the US in the first day. One million were sold in Britain, more than twice as many as Prisoner of Azkaban sold in its first year!
It's smashed records as fans all over the world race to get their hands on book five.
One US bookstore, a branch of Barnes and Noble, said the book was flying off their shelves at a rate of more than 80 per second!
It looks like OOTP is going to be 10 times more popular than the Goblet Of Fire, their spokesman said.
Bookshops everywhere opened their doors at midnight on Friday so the desperate fans could get hold of the book as soon as it went on sale.
OOTP has already broken online records after becoming the most pre-ordered book ever. Amazon took a whopping 1.3 million orders for the book before it even came out.
Fans everywhere are eagerly getting through the 766 pages to find out which character dies, and why Voldemort and Snape hate Harry so much.