It is a day to celebrate books and reading and school children typically dress up as their favourite book character.
Have a look at some of the children in Derry dressed up today.
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IN PICTURES: Derry children dressed up for World Book Day
By Daire Ní Chanáin
Published 3rd Mar 2022, 17:23 BST
Updated 3rd Mar 2022, 17:39 BST
World Book Day is celebrated throughout the world today, Thursday March 3.