World Book Night is an annual celebration dedicated to spreading the love of reading, person to person.
Each year on April 23 –Shakespeare’s birthday– tens of thousands of people in the U.S. go out into their communities and give a total of half a million free World Book Night paperbacks to light and non-readers. For more information about World Book Night, please visit the About Us section of the website.
[ETA] and from under the website's "Our History" section:
"Each year, World Book Night is celebrated around the world on April 23.
April 23 is the UNESCO International Day of the Book, as well as Shakespeare’s birthday. It was also chosen in honor of Miguel de Cervantes, who died on April 23, 1616 (the same day as Shakespeare). In the Catalan region of Spain, the day is celebrated by giving a book and a flower to a loved one.
World Book Night was the product of a round table discussion at London’s Book Industry Conference in May 2010, the purpose of which was to imagine a way to encourage more adults to read. What better way to spread a love for reading than to inspire passionate readers to go out into their communities and share copies of their favorite books with those who don’t regularly read? Giving is an incredibly powerful part of our culture—and culture, art, and a writers’ talent are all themselves ‘gifts’.
World Book Night was first celebrated in the UK and Ireland in 2011; in 2012, it was also celebrated in the USA and Germany."