Only a recent celebration—the commemoration was founded on April 23, 1995—the annual event is organized by the United Nations Education, Scientific and Cultural Organization, better known as UNESCO.
April 23 was picked randomly, but it's also the date widely believed to be the birthdate of William Shakespeare. Though no record exists of his birth, there is a record of his baptism in Stratford-upon-Avon on April 26, 1564. This is also the day that Shakespeare died—April 23, 1616. It's also believed that Miguel de Cervantes had died on this date in 1616, though some historians argue that he died the day before. Other important literary figures were also born on this day, including Vladimir Nabokov and Garciliaso de la Vega.
Ironically, it was on World Book Day only a year ago that copies of Sherman Alexie's "The Absolutely True Diary of a Part-Time Indian" were freely distributed in a Meridian Park after the Meridian school district had shelved the book, taking it from its reading list after a complaint.
Ultimately the book made it back to the West Ada School District's supplemental reading list in September 2014, but only with some strict conditions: students must have a permission letter signed by parents and the book is not allowed to be read aloud in class.