Leviticus 25:8-13 sets out the most ambitious economic provision in the Hebrew Bible. After seven sabbaths of years, forty-nine, the fiftieth year is hallowed, the ram's horn is sounded on the Day of Atonement, liberty is proclaimed throughout the land, and every person returns to their holding and to their family. Land sold reverts to the household that held it. Israelites who have sold themselves into service go free.
The logic is stated in the text: the land is not to be sold in perpetuity, for the land is God's and the people are tenants on it. What is bought and sold is therefore not the land but the number of harvests remaining until the Jubilee, and the price is to be adjusted accordingly. This is a legal system designed to prevent the permanent accumulation of land in few hands, and it is unusual enough among ancient legal codes to be worth stating plainly.
Whether it was ever kept is another matter and is genuinely contested. There is no unambiguous record of a Jubilee year being observed. Rabbinic tradition holds that the Jubilee applied only when all the tribes were settled in the land and lapsed with the Assyrian deportations. Some historians treat the legislation as a utopian or priestly programme rather than a practised institution; others argue for a limited historical application. The text itself anticipates objections about the seventh and fiftieth years falling consecutively and answers them.
The word Jubilee comes from the Hebrew yovel, the ram's horn sounded to announce it, and passed through the Latin iubilaeus into the Christian jubilee years, the first proclaimed by Boniface VIII in 1300.