The setting inside the book
Deuteronomy does not give a modern calendar date. It places its speeches east of the Jordan, in Moab, after Israel's long wilderness journey and before the people enter the land God promised them. Moses is speaking to a new generation, urging them to remember God's faithfulness and obey him when they settle in Canaan (Deuteronomy 1:1-3).
That setting matters. The book reads like farewell teaching from an ageing leader who knows he will not cross the river with the people. Its laws, warnings, songs, and blessings are tied to that moment, not simply presented as detached rules (Deuteronomy 31:1-3).
These be the words which Moses spake unto all Israel on this side Jordan in the wilderness, in the plain over against the Red sea, between Paran, and Tophel, and Laban, and Hazeroth, and Dizahab.
What Deuteronomy says about Moses writing
The book explicitly says that Moses wrote down the law and gave it to the priests and Israel's elders (Deuteronomy 31:9). Near the close, it again says he finished writing the words of the law in a book, which was then placed beside the ark of the covenant as a witness for the people (Deuteronomy 31:24-26).
For this reason, the traditional Jewish and Christian understanding is that Moses wrote the central material of Deuteronomy. If one follows a traditional dating of the Exodus, that would place its main writing either in the fifteenth or thirteenth century BC, depending on how the biblical chronology is understood. Scripture itself is clearer about the setting than about a numbered year.
And it came to pass, when Moses had made an end of writing the words of this law in a book, until they were finished,
What about Moses' death?
Deuteronomy's final chapter records Moses' death and burial (Deuteronomy 34:5-6). Since Moses could not describe his own death afterwards, many readers who hold to Mosaic authorship believe a later servant of God, perhaps Joshua or another inspired writer, supplied this closing account.
That need not erase Moses' role in the rest of the book. Ancient books could preserve a principal author's work while including a brief concluding note. The text itself carefully distinguishes Moses' written law from the report of what happened after his death.
Why do dates differ?
Some modern scholars argue that Deuteronomy was composed or substantially shaped much later, often connecting it with the book of the law found during King Josiah's reforms. That event appears in the history of Judah centuries after Moses' day (2 Kings 22:8-11). Other Christians see that discovery as the recovery of an older Mosaic book, not evidence that it was newly written then.
There is real disagreement here. Still, readers from both views can begin with what Deuteronomy plainly asks of Israel: love the Lord wholeheartedly, teach his words to the next generation, and live faithfully in the land (Deuteronomy 6:4-7). Reading the book for yourself is the best place to start.
Hear, O Israel: The Lord our God is one Lord: