The fifth book of the Old Testament is Deuteronomy, which contains 11 letters. It is the fifth book of the Torah, and is a collection of laws and stories that were given to Moses by God. It is believed to have been written in the 6th century BCE, and is the second of five books of the Torah that are collectively known as the Pentateuch. Deuteronomy is also known as Mishneh Torah, which means 'repetition of the law'. It is an important part of Jewish and Christian religious traditions.