The 'Christmas book flood' is a term used in Iceland for the annual release of new books occurring in the months before Christmas. These books are then purchased as presents to be gifted on Christmas Eve. This tradition makes books the most popular Christmas gift of the country. The tradition extends into the night, when Icelanders will often read their new books and drink hot chocolate.

Newly published books are listed in an annual catalogue called the 'Journal of Books' that is distributed to all households for free. The release of the Journal is the beginning of the book flood, signifying the start of the holiday season. The tradition comes from both Iceland's centuries-long literary history and the state of the economy during WWII, when strict currency restrictions limited the amount of imported giftware. Given that restrictions on imported paper were more lenient than on other products, books became and stayed the Christmas gift of choice.

More Info: en.wikipedia.org