Having built up a huge following over the past few years this is one popular event, taking place in schools, hospitals, hospices and pre-schools all over the UK on 3rd March 2016, with thousands of children getting involved - although, you probably didn't need us to tell you that.
Here's everything you need to know...
The best part of the day (in our opinion) is coming up with a literary-themed costume with our kids. The excuse to talk about all the books they've read and loved over the past year is a moment we always look forward to and their imaginations never cease to amaze us (The Twits, anyone?!). With that in mind we've put together a gallery of the absolutely BEST costumes we've ever seen from some of our favourite bloggers. From a clever Paper Bag Princess idea which takes nothing but some wrapping paper to The Lord Of The Rings Hobbits which needs real sewing expertise, we've got all levels of commitment covered.
And once your child has settled for a character, don't forget to share your snaps of them in their costume with us on Facebook, Twitter or Instagram - we love seeing all the amazing ideas you come up with for World Book Day using the #GTKWorldBookDay. And we're not making any promises but there just might be a prize in it for the best entries!
Ok, there are definitely prizes for the best entries. From scooters for your whole family to a dressing up box for your class - there plenty of opportunities to win!
If you're still struggling for ideas then why not have a peak at the list of 50 books every child should read before they're 16. It was drawn up by Sainsbury's last year in honour of World Book Day itself and includes all the classics. If you spot a book your child loves then that is often a great way to come up with costume ideas. Some of our personal favourites are the Dr. Zeus characters.
Along with the day comes all other sorts of fun including £1 book tokens from the National Book Tokens people, publishers and sellers. In partnership with schools all over the UK, World Book Day help provide more than 14 million £1 tokens for some of the best kids' books of the moment. That's nearly one for everyone under the age of 18 in the whole of the UK and Ireland! There's even the option to use your token to buy a full-priced book with a £1 off.
If you've got a bit of a bright spark in your family then you're going to want to do this. World Book Day have organised a quiz for all little book worms to get involved with on the 22nd February. And this isn't any old quiz, it's a world record breaking quiz. They're aiming to break the record for the most people participating in a simultaneous book quiz at one time. You'll have to be quick though, registration closes on the 5th of February.
And they haven't forgotten little artists either - there's a chance to win prizes for coming up with a book token design. This can be organised through your school so ask your child's teacher if you're interested in getting your mini Monet involved.
World Book Day is the perfect time to get your little one into reading - plus World Book Day have extended their reach in recent years to include nursery children too. To inspire your toddlers to love reading we've put together a guide on the best books for children between 0-5 years old.
Once little ones have started reading at school they'll be progressing quickly. One of the best ways to keep them motivated and constantly improving is to make sure they have plenty of fun books to get their teeth into. This round up includes classics old and new to appeal to all kinds of children. Plus, with so many ideas there's sure to be something that'll spark your imagination for a World Book Day costume.
Not all high schools take part in World Book Day but if they do then your teen is going to need a cool costume to impress the rest of the class. Get some more grown-up costume inspiration from this round up of cult classic books.
For a final flourish of inspiration let us point you to the most magical children's book quotes of all time. There is inspiration in abundance, as well as a good dose of 'why aren't I this profound?'.
Oh, sorry, we're actually not finished. We believe it's a crucial rite of passage for every child to be an expert den-maker. These beautiful dens are the perfect place to cosy up and read your favourite book together.
So, with all that to look forward to we bet you can't wait to get started. (Or is that slightly over selling it for having to spend frantic evenings making a costume that will never look as good as it did in your head?!) Either way, we're sure World Book Day will be as fun as ever this year. Don't miss our fab World Book Day competition too - here are some of the brilliant entries we've had...