23 April is a symbolic date for world literature for on this date in 1616, 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. In this respect, UNESCO created both the World Book and Copyright Day and the UNESCO Prize for Children's and Young People's Literature in the Service of Tolerance.
http://www.un.org/depts/dhl/book