Mosaic authorship is the Jewish and Christian tradition that Moses was the author of the first five books of the Hebrew Bible/Old Testament (the Torah). The books do not name any author, as authorship was not considered important by the society that produced them, and it was only after Jews came into intense contact with author-centric Hellenistic culture in the late Second Temple period that the rabbis began to feel compelled to find authors for their scriptures. The tradition probably began with the law-code of Deuteronomy, and was then gradually extended until Moses, as the central character, came to be regarded not just as the mediator of law but as author of both laws and narrative.
It was already common practice to refer to the five books as the "Law of Moses" by the 1st century CE, but the first unequivocal expression of the idea that this meant authorship appears in the Babylonian Talmud, an encyclopedia of Jewish tradition and scholarship composed between 200-500 CE. The rabbis noticed and addressed such issues as how Moses had received the divine revelation, how it was curated and transmitted to later generations, and how difficult passages such the last verses of Deuteronomy, which describe his death, were to be explained. It remained the accepted belief of both Jews and Christians until the European Enlightenment and the systematic study of the five books led the majority of scholars to conclude that they are the product of many hands and many centuries; nevertheless, the role of Moses is an article of Jewish faith according to the 8th of Maimonides' 13 Principles of Faith, and for some Christian Evangelical scholars it remains crucial to their understanding of the unity and authority of Scripture.
The Torah (or Pentateuch, as biblical scholars sometimes call it) is the collective name for the first five books of the Bible - Genesis, Exodus, Leviticus, Numbers, and Deuteronomy. It forms the charter myth of Israel, the story of the people's origins and the foundations of their culture and institutions, and it is a fundamental principle of Judaism that the relationship between God and his chosen people was set out on Mount Sinai through the Torah.