World Book and Copyright Day (also known as International Day of the Book or World Book Days) is a yearly event on 23 April, organized by UNESCO to promote reading, publishing and copyright. The Day was first celebrated in 1995 and in 2012 the UK World Book day was celebrated on 1 March 2012.
World Book Day was celebrated for the first time on 23 April. The connection between 23 April and books was first made in 1923 by booksellers in Spain as a way to honour the author Miguel de Cervantes who died on that day.
This is why UNESCO chose this date to pay a worldwide tribute to books and their authors on this date, encouraging everyone, and in particular young people, to discover the pleasure of reading and to gain a renewed respect for the extraordinary contributions of those who have furthered the social and cultural progress of humanity.
Source : Wikipedia & UNESCO