A very hungry caterpillar, Dorothy or maybe one of the Twits... deciding who to dress up as for World Book Day can be tricky.
Thousands of you are going to school dressed as characters from your favourite books to join in with the World Book Day celebrations.
The yearly event celebrates authors, illustrators, books and reading and is marked in more than 100 countries across the globe.
Newsround wanted to know what you are doing to celebrate World Book Day 2016.
This page is now closed. Thank you so much for sending us all of your wonderful photos and messages.
Your World Book Day photos and comments
Here are sisters Taylor and Madison from Birmingham, England. Taylor is the Queen of Hearts from Alice in Wonderland. Madison is Dorothy from the Wizard of Oz!
Mitchell from Larbert is his favourite book character the Stick Man
Miko and Karl from London are the Star Wars characters R2-D2 and BB-8
Kush from London is ready to cast some spells as Harry Potter
Ben and Oliver from Weston-super-Mare are the Weasley Twins from Harry Potter
Tom and his sister Anna sent us this photo from Ayrshire, Scotland. Tom is Saucepan Man from the Enid Blyton Magic Faraway Tree books, and Anna is Hermione Granger from Harry Potter
Murphy from West Sussex wanted to dress up as Sepron the Sea Serpent from the Beast Quest books. That's one impressive outfit!
Here's Lydia as Miss Root from the David Walliams's Demon Dentist, and Jonah as a turtle.
Twins Hannah and Jenson are dressed as characters from the book 'Kids in the Cockpit'
Here's Anthony from Chichester as Pierre the Maze Detective
Coco is dressed as Astrid from How To Train A Dragon. Coco and her mum made this whole costume from felt, clay and silver card for the shoulder pads.
Say hello to the wonderful staff and children of Great Ballard School in West Sussex who all got dressed up for World Book Day!
Kai from Eastbourne wanted wanted to be Fred from Scooby Doo because he is a comic book charater. He wanted to give a big shout out to his swing class at school because they watch Newsround everyday at end of class. Well, thank you very much!
Somewhere under that brilliant costume of Greg from Diary of a Wimpy Kid is Ella from London
Harry from Birmingham loves Mr Tumble so he decided to dress up like him
Miss Viney and her fellow teachers at school got into the spirit and got dressed up as Hagrid, Lord Voldermort and Dobby from Harry Potter
Ruby from London taking her role seriously as the Queen of Hearts from Alive in Wonderland. Her mum made this costume!
Talia from Dorset dressed as The Lion, The Witch and The Wardrobe for World Book Day. Talia loves to read and has a huge book collection. Her favourite author is Roald Dahl.
Mrs G from Great Ballard School in West Sussex looks like she's having fun as Gangsta Granny
Here's May as Padme from Star Wars, and yer younger sister Caitlin as Peppa Pig
Jack from Evesham is the boy wizard, Harry Potter. Great glasses and scarf!
Jack from Coulsdon in England is the Boy in a Dress
Students and teachers at Farlington Prep School in Horsham in England got dressed up as their favourite book characters
Bridie from Grimsby in England is ready to be a hero as Katniss Everdeen from The Hunger Games books
Cara from Troon in Scotland is dressed up as Sophie from The Tiger Who Came to Tea
It's not just school kids who join in on World Book Day. Check out this little one dressed up as Piglet from Winnie the Pooh!
Mrs Gammond's class at Weston-under-Penyard School in Herefordshire celebrated by dressing up, taking part in book quizzes and sharing stories across the school.
Freyja and Eilidh from Glasgow, Scotland, are Thing 1 and Thing 2 from the Dr Seuss books
Joe from Ruan Minor is the Boy in a Dress, the character written by author David Walliams
Keris from Long Eaton is Lenny from the book 'Lenny the Lazy Puppy'
Milla from Somerset is Ruby Redfort, the super sleuth written by Lauren Child
Luke, Oliver and Erin are from Clacton-on-Sea. They are dressed as (left to right) Little Pig, William Beech from Goodnight Mr Tom, and Harry Potter
Jake from Southampton looks like he is loving his World Book Day costume! He's dressed as Big Skeleton from Funnybones
Darcey from Doncaster went to school as the Mad Hatter from Alice in Wonderland. This is the first time she's had chance to do world book day
Charlie and Cairo look brilliant as Thing 1 and Thing 2 from the Dr Seuss books
Awais from Bradford is Freddy from 'Five Nights at Freddy's'. Also, that looks like a great programme on your TV!
Archie and his brother Ellwood dressed up for World Book Day. Archie is Jack and the Beanstalk and Ellwood is Sam I am
Owen is dressed up as Mr Stink and his big sister Tia is Gansta Granny. They're both from Billinge in England
Nabil from London as Edmund from The Chronicles of Narnia
Teachers from St George's CE Primary School in Westhoughton got their Gangsta Granny costumes on
Charlotte lives in Abu Dhabi, United Arab Emirates, and dressed up as the Demon Dentist for World Book Day
Here's Noah from Shropshire in England as Wally
'Alas poor Yorick I knew him well!' Here's Jack and Archie from Salisbury as the skull and Hamlet from Shakespeare's classic play
Eva's favourite book is the tooth fairy!
Emily chose a traditional character, Cinderella, for her World Book Day outfit
Dominic from Chorley is Greg from Diary of a Wimpy Kid
James from Belfast in Northern Ireland was set an Extreme Reading Challenge by his school. Everyone was asked to think about a different, exciting, fun and SAFE place to enjoy a book and take a photo. Here he is reading a book on his climbing wall!
Jacob from London is Mr Gum
Lorna from Sutherland is dressed as George from Roald Dahl book George's Marvellous Medicine
Theo from Northamptonshire is David Walliams's Boy in a Dress
Betty from London is the Butterfly from Very Hungry Caterpillar
James and Olivia from Preston dressed as Wally and Wenda from 'Where's Wally'
Lacey from Lancashire is the Goblin King from her favourite book and film Labyrinth
Mr Clark's class at Moorlands Junior School in Sale had a great World Book Day. Some of the costumes are James Trotter and his giant peach to Mrs Fox and Greg from Diary of a Wimpy Kid
Jamie from Crawley dressed up as Horrid Henry and he even made his own tricks and treats book
Mali from London is Professor Trelawney from the Harry Potter books
Rory from Stourport-on-Severn is the Artful Dodger from Oliver Twist
Tom from Exeter is Bond...James Bond
Teachers from St Katherine's School Maths Department in Somerset dressed up as characters from Alice in Wonderland
Check out Theo from the Wirral's brilliant SpongeBob SquarePants costume!
Efan from London went to school as Hagrid from Harry Potter
Ava from Worcestershire is looking cosy as The Tiger Who Came to Tea
Anthony from Croydon is dressed up us a Centaur from Harry Potter
Wilbur from Coleraine in Northern Ireland is Roald Dahl's Fantastic Mr Fox
Raphael from Basingstoke has dressed as Prince Aleksandar of Hohenberg from Scott Westerfeld's novel 'Leviathan'
Zachary from Basingstoke has dressed as Usagi Yojimbo, the Rabbit Ronin, from Stan Sakai's series of graphic novels
Chloe from Newcastle in England is Gangster Granny
Daniel from Barnet loves David Walliams books so he went to school as the Boy in a Dress
Caitlin and Emily from Saffron Walden in England have made hats representing their favourite books and wore them to school for a hat parade. Caitlin's hat is Harry Potter and Emily's hat is Rose by Holly Webb
This is Charlie from Bolton and here she is as Alice in Wonderland, her favourite book ever
Ellis is 9 and from Leeds in England. She loves reading Shakespeare so is going to world book day as Cleopatra!
Brenna from Braintree in England is feeling magical as Hermione from Harry Potter
Jessica Jayne from Coventry in England is dressed as a very cool Willy Wonka. We're loving those glasses in the Newsround office!
Oliver and Summer from Hampshire in England love books! Oliver even got his hair sprayed black to be Harry Potter as he didn't want to be mistaken for Draco Malfoy! Summer makes the perfect Little Miss Sunshine
Jersey from Pontypridd in Wales chose The Rainbow Fish for World Book Day!
Lilly and Lucy are the best of sisters like Anna and Elsa from Disney's Frozen
This class at Eastwick School in Surrey do Charlie & The Chocolate Factory...with two witches & a super hero thrown in too!
Southfields Primary School in Coventry are celebrating World Book Day. They've had Buddy Reading, written book reviews and other fun reading activities.
Charlie is going to school as Roald Dahl's Mr Twit, and his sister is dressed up as the character from 'There was an old lady who swallowed a fly'
Cairo from Scarborough in England is dressing up as Willy Wonka from Roald Dahl's Charlie and the Chocolate Factory
Joshua from Luton is dressed up as his favourite book character, Stick Man
At Alfie's and Ellie's school in London, kids are dressing up vegetables as their favourite book characters!
Abby from Northern Ireland dressed up as Princess and the Pea
Oscar and Felix are from Darlington in England and their favourite book is anything to do with Tintin. Here they are as the characters Thomson and Thompson
Anna from Icklingham in England broke her ankle two weeks ago, so she decided to dress up as Tiny Tim from 'A Christmas Carol'
Here's Keaton from Manchester as an Oompa Loompa from Roald Dahl's Charlie and the Chocolate Factory
Ben from Northern Ireland is the Stick Man
Harry from Nottingham in England is going to school as Gideon from the book Hetty Feather by Jacqueline Wilson. His school will be doing lots of book activities and his little sister has to wear pyjamas!
Miles from Nottinghamshire in England has been ready since 7am. He is really excited and wishes everyone a really happy world book day!
Nancy from London couldn't choose just one character from so many lovely books...so she decided to have a few from all over the world!
Megan from Pontypridd, Wales, is Mary Poppins because her mum says she's 'practically perfect in every way'
Benjamin from Leamington Spa in England is a very smart Willy Wonka from Roald Dahl's Charlie and the Chocolate Factory
Aron from London, England, dressed up as 'The highway rat'. It is his favourite book. Aron and his mum made a sword, a tail and added a feather to his old pirate hat
Reuben, Matilda and Harriet love Alice in Wonderland and wanted to take this opportunity to all dress up as characters from the same book, as it is the first and last World Book Day they will be sharing before Reuben goes to secondary school
Shayla from Stafford will be trying her best to hide as Where's Wenda
Maisie, Josh and Hollie from Devon in England are dressed up as Little Red Riding Hood, Captain America and Goldilocks for World Book Day
Sophia from London, England, is going to school dressed as Spiderman
Diya from London, England, is going to school as Jacqueline Wlson's Hetty Feather character. At her school, kids get a form prize for most innovative dress and they have lots of drama workshops and fun fun fun!
Kiedan-Lee from Bolton in England dressed up as Roald Dahl's Fantastic Mr Fox
Poppy from West Sussex in England is Alice from Lewis Carroll's Alice in Wonderland
Here's Lani from Nottingham, England, dressed up as Hermione from Harry Potter
Kailan from Nottingham is dressed as an Oompa Loompa for World Book Day. He loves Roald Dahl's Charlie and the Chocolate Factory!
Here are Saskia and Isla as Matilda and Pippi Longstocking with Mr Nelson, Pippi's pet monkey. The sisters are from Portishead in England.
Isabelle from Hadfield in England chose Sophie from The BFG as she loves all Roald Dahl's stories. She was Mrs Twit last year!
Here's Eva from Somerset, England, dressed as Little Red Riding Hood with Mog the wolf disguised as Grandma!
We celebrated World Book Day yesterday because it was Dr. Seuss's birthday! We call it Read Across America Day. We took part in several Dr. Seuss activities, we had mystery readers, which included Marines and the local university's basketball players, and in the afternoon we "Dropped Everything and Read". It was great fun! (Miss Marsh's 4th Grade Class, Union Elementary School in North Carolina, USA)
I am doing 'drop everything and read' at school - every time a bell goes we have to read a book for 5 minutes. (Grace, Linlithgow, Scotland)
I am Alex Rider for the day. I have my spy gadgets at the ready! (Uzayr, Stratford, London)
Unfortunately, my school forgot to send out a letter about dressing up for world book day so we are just bringing in our favourite book and it's my last year there! (Sian, Hull, England)
My favourite book is Matilda and my brother's is Avengers Assemble. (Amrita, Luton, England)
Year 7s have dressed up today and even some teachers! In Mrs Sweeney's class we have a Cat in the Hat, Mary Poppins and a couple of Little Red Riding Hoods as well as a lot more. (Mrs Sweeney from St John Bosco Arts College, Liverpool, England)
I am dressing up as Lisa out of The Boy in the Dress. (Divina, Sheffield, England)
My brother and I are dressing up as Little Red Riding Hood and Clark Kent. (Holly and Eden, England)
Our school is running a competition where you have to take a picture of yourself reading in an weird place. (Alice, Hampshire, England)
For world book day I'm dressing up as Geek Girl by Holly Smale! I can't wait!!! (Mahnoor, Stratford, England)
Everyone at our school is dressing up as Roald Dahl characters. I am dressing up as an Oompa Loompa. (Frances, Tamworth, England)
I'm dressing up as the Demon Dentist and my favourite author is Kate Camilo. (Citrina, London, England)
I'm dressing up as Judy Moody for World Book Day (Jessica, Glasgow, Scotland)
I am going to be Mr Stink from the book by David Walliams. (Ellie Mai, Harrogate, England)
I'm getting a free £1 book voucher and a story teller is going to come in on Monday. (Holly, Northern Ireland)
I'm going as Henry VIII from Horrible Histories by Terry Deary. (Nathan, Derbyshire, England)
I am not going to dress up today but seeing all of these costumes makes me want to! (Jordan, Broxburn, Scotland)
We get to dress up, bring in a book and our class are doing a Roald Dahl 'Revolting Rhyme' performance. (Innes, Sunderland, England)
I have met an author and got a new book and tomorrow I will see another author. I love reading books especially the Harry Potter books, JK Rowling is by far my favourite author and my inspiration. (Mia, London, England)
My little sister is dressing up for mad hatter for world book day. (Amy, Sheffield, England)
I'm dressing up as Hannah from the Forever Whale by Sarah Lean (Lucia, Kettering, England)
I'm dressing up as Katniss Everdeen from The Hunger Games. (Niamh, Shropshire, England)
I'm dressing up as Granny out of Gansta Granny by David Walliams. (Abbie, Derbyshire, England)
I am dressing up as Grandpa, a World War Two flying ace, from Grandpa's Great Escape and we are doing a book swap. (Nasser, Eastbourne, England)
I'm going to be going as Hetty Feather. (Skylar, Cheshire, England)
I'm dressing up as Tracy Beaker and writing a short story at school. (Tegan, Scotland)
For World Book Day I am dressing up as Hetty Feather, unfortunately my class has a science morning at our secondary school so we can't go to school dressed up but I can change at lunchtime. (Ell'e, Lincoln, England)
I'm dressing up as Greg from Diary of a Wimpy Kid. (Asa, Kidlington, England)