The world's best-selling and most widely distributed book is the Bible. It has an estimated 2.5 billion copies sold since 1815. It has been translated into 2,233 languages and dialects. The Christian Bible as we know it today is in two parts, the Old Testament and the 27 books of the New Testament, written between 50 and 150 AD. The latter and some of the additional books were originally written in Greek.