A million copies of Harry Potter and the Philosopher's Stone film could be sold on video and DVD on Saturday alone.
Retailers think it'll become the biggest seller of all time, smashing the record held by Titanic.
HMV's Oxford Street store in London opened to big queues at midnight to sell the first copy.
The shop was transformed for the event by wizards, witches and owls.
First copy in Britain
And Asda stores had a special Hogwarts Express checkout between checkouts nine and 10 - just like Platform nine-and-three-quarters!
Thousands of fans have already ordered their copy over the internet.