The Quran is believed to be the words straight from God, Allah. It is the book that the Muslims use as a guide full of religious texts of how they should live their lives.
The Harry Potter series has not only sold millions of books, but also went on to be one of the most popular film series of all time.
This book sold over 820 million copies in the past five decades. It is also known as The Little Red Book.
The journey of Frodo Baggins has been read by so many people that in the last 50 years, it has sold 103 million copies.