It's the 20th anniversary of World Book Day, when children celebrate their favourite books and authors around the world.
It's marked in more than 100 countries, as schools and teachers encourage students to dress up as famous literary characters.
We've picked out the most inventive and adorable costumes from kids in UK schools this year.
But for the adults out there, can you remember the opening lines from the classics? From J.K. Rowling's Harry Potter to a Roald Dahl classic, see how many you can get right.