Deuteronomy, Hebrew DEVARIM ("Words"), fifth book of the Old Testament, written in the form of a farewell address by Moses to the Israelites before they entered the Promised Land of Canaan. The speeches that constitute this address recall Israel's past, reiterate laws that Moses had communicated to the people at Horeb (Sinai), and emphasize that observance of these laws is essential for the well-being of the people in the land they are about to possess. The title Deuteronomy, derived from Greek, thus means a "copy," or a "repetition," of the law rather than "second law," as the word's etymology seems to suggest.

Although Deuteronomy is presented as an address by Moses, scholars generally agree that it dates from a much later period of Israelite history. An early edition of Deuteronomy as it exists today has been identified with the book of the Law discovered in the Temple of Jerusalem about 622 BC (2 Kings 22:8; 2 Chronicles 34:15). This early edition, corresponding roughly to chapters 5-26 and 28 of Deuteronomy as it now stands, expresses a cultic liturgy. Chapters 5-11 contain an introductory speech by Moses, largely hortatory. In chapters 12-26 laws are reiterated that the people are exhorted to obey. The section closes with a report of the formulation of a Covenant between God and his chosen people. Chapter 28 recounts in elaborate detail the blessings or curses that will come upon the people, depending on their response to laws that explicate their covenantal obligations. This arrangement of materials corresponds to the liturgy of Covenant renewal festivals that were celebrated in Israel's premonarchic period. Within this cultic context very ancient laws were preserved and transmitted.

To this original core of materials other materials were added by interested parties in the years following the reforms instituted by King Josiah (reigned c. 640-609 BC). The final form is due to the work of a historian who added, among other things, a second introduction (chapters 1-4) and made Deuteronomy the book of first principles for his history of the Israelite people in the land of Canaan. Deuteronomy might thus be viewed as the first part of the history that follows, rather than as the last book of the Pentateuch, the generally accepted order most scholars prefer.