23 April is a symbolic date for world literature. It is on this date in 1616 that Cervantes, Shakespeare and Inca Garcilaso de la Vega all died. It is also the date of birth or death of other prominent authors, such as Maurice Druon, Haldor K.Laxness, Vladimir Nabokov, Josep Pla and Manuel Mejía Vallejo.
It was a natural choice for UNESCO's General Conference, held in Paris in 1995, to pay a world-wide tribute to books and authors on this date, encouraging everyone, and in particular young people, to discover the pleasure of reading and gain a renewed respect for the irreplaceable contributions of those, who have furthered the social and cultural progress of humanity. With this in mind, UNESCO created the World Book and Copyright Day.
Additional information is available here.