The Extentes are lists of Crown Rights and Revenues in Jersey. New Extentes were compiled from time to time once the previous Extente had become out of date. Between 1876 and 1883 the Société published some of the surviving Extentes: those compiled in the years 1274, 1331, 1528, 1607, 1668, and 1749.
These documents contain much detail about the rentes and revenues payable to the Crown, including the names of some tenants and their feudal obligations, and lands and fiefs which had reverted to the Crown, for one reason or another. Some of the private Fiefs and Seigneurs are listed, with their feudal obligations, but not their tenants.
The Extentes are of fundamental importance for any study of the island's population and land use.