Image caption The films launched the careers of Emma Watson, Daniel Radcliffe and Rupert Grint
It’s exactly 20 years since Harry Potter and the Philosopher’s Stone came out.
The first hardback run, on 26 June 1997, was just 500 copies. The series as a whole has now sold more than 450 million books around the world.
To mark the occasion, Facebook has launched an Easter egg which fills the screen with sparks from a wand.
Twitter has got on board too, by making a special emoji of Harry’s trademark glasses.
Here’s how you get them.
Image caption We couldn’t resist giving it a go
On Facebook all you have to do is type “Harry Potter” into a status or comment, followed by the name of one of Hogwarts’ houses.
In case you’ve forgotten – you’ve got four to choose from: Gryffindor, Hufflepuff, Ravenclaw and Slytherin.
The text will then change colour and when you click on it a wand will appear and shoot sparks across the screen.
On Twitter, an emoji appears when people type the hashtag #HarryPotter20.
Fans have been using it to share their memories of the series.
Of course, there aren’t just JK Rowling’s books to talk about. The series also spawned one of the most successful film franchises ever.
The final instalment, Harry Potter and the Deathly Hallows Part 2, is the eighth-highest grossing movie of all time.
The franchise continued in 2016, with the spin-off Fantastic Beasts and Where to Find Them.
JK Rowling says she has plans for five more Fantastic Beasts films.