The most expensive book in the world is believed to be the Bay Psalm Book, which was sold at an auction in 2013 for $14.2 million. The book was printed in 1640 and is the first book ever printed in what is now the United States.

The oldest book in the world is believed to be the Epic of Gilgamesh, which is estimated to have been written around 2100 BC. It is an ancient Mesopotamian poem written in cuneiform script on clay tablets.

The Bible is the best selling book of all time, having sold billions of copies in hundreds of different languages. Other popular books include J.K Rowling’s Harry Potter series, which has sold over 500 million copies, and Dan Brown’s The Da Vinci Code, which has sold over 80 million copies.