On Thursday 7 March, thousands of you up and down the UK will be dressing up for World Book Day.
It's a big international event, started 22 years ago, celebrating books and reading.
Its aim is to give every child a book of their own (you can find out how it does this below).
It's organised by a charity and takes place in more than 100 countries all over the world, although some other countries actually celebrate it in April.
World Book Day is the biggest celebration of its kind. The aim of it is to celebrate authors, books, illustrators and - of course - reading!
To help young people to do that, book tokens are given out at schools, including some nurseries and secondary schools.
Those who are schooled at home can also get the £1 tokens, which can be used in one of the thousands of bookshops and supermarkets which are taking part to get a book for free (there are 12 books to choose from, one of which is written by the Children's Laureate Lauren Child).
Around 15 million tokens are given out, which works out as one for nearly every child aged under 18 in the country.
There are lots of different ways to celebrate World Book Day.
Many schools have special events planned for it - whether it's a trip to the local library, classroom displays of famous literary characters or book-themed activities in lessons.
While that may be a very fun part of the day, it's not what it's all about. The main aim is to get young people to read and love books.
But it's still pretty great to go to lessons as Willy Wonka, Paddington Bear or Gangsta Granny!
Often schools will ask pupils who come in costume to donate money to a charity, such as Book Aid International, which means books can be sent to children in other countries.
There are lots of reasons that people believe that World Book Day is important.
Some children might not like reading or struggle with it, so it can be an encouraging event for them.
Others may not have their own books at home, so the tokens can provide them with an opportunity to get their first book. The World Book Day charity did some research in 2016 and found that for 1 in 4 kids, the book they bought with their token was the first one they owned.
It also found that the day inspired lots of young people to read more than they may already do.
We want to know what you think about World Book Day.
Do you enjoy it? Do you think it's important and why? What will you be doing to mark it this year? Let us know in the comments below.
Not only that, though. We want to see all of your amazing costumes!
There were some seriously impressive World Book Day costumes last year. Can you top them this year, we wonder?