Deuteronomy (Greek deuteronomion,Δευτερο-νομιον "second law") is the fifth book of the Hebrew Bible and of the Old Testament. In form it is a set of three sermons delivered by Moses reviewing the previous forty years of wandering in the wilderness; its central element is a detailed law-code by which the Children of Israel are to live in the Promised Land.

In theological terms the book constitutes a covenant between Yahweh, the God of Israel, and the "Children of Israel", his "chosen people"; this is the culmination of the series of covenants which begins with that between Yahweh and all living things after the Flood (Genesis 9). One of its most significant verses constitutes the shema ("Hear, O Israel, the Lord (YHWH) is our God, the Lord (YHWH) alone!"), which today serves as the definitive statement of Jewish identity.

The bulk of the book appears to have been composed in the late 7th century BC, during the religious reforms carried out under king Josiah of Judah, with later additions from the period after the fall of Judah to the Neo-Babylonian empire in 596 BC. Its essential concerns mirror the thrust of Josiah's reforms: Yahweh is to be accepted as the sole God of Israel, and worshipped only in one place.