The feudal concept of demesne is a form of manorial land tenure as conceived in Western Europe, initially in France but exported to England, during the Middle Ages.

Demesne land was all the land, not necessarily all contiguous to the castle, that was retained by the lord for his own use as distinguished from that "alienated" or granted to others (alienii) as tenants, whether irrecoverable freehold or leasehold, commonly for a lifetime. Initially the demesne lands were worked on the lord's behalf by villeins or by serfs, in fulfillment of their feudal obligations. As a money economy returned, region by region, in the later Middle Ages, the serfs' corvée came to be commuted to money payments. When demesne lands come to be cultivated by paid laborers, we have arrived at Early modern Europe. Eventually many of the demesne lands were leased out either on a perpetual, and therefore hereditary, or a temporary, and therefore renewable, basis so that many peasants functioned virtually as free proprietors after having paid their fixed rents. In times of inflation or debasement of coinage, the rent might come to represent a pittance, reducing the feudal aristocrat to poverty among a prosperous gentry.

In English Common Law the term ancient demesne, sometimes shortened to demesne, referred to those lands that were held by the crown at the time of the Domesday Book. The term demesne also referred to the demesne of the crown, or royal demesne, which consisted of those lands reserved for the crown at the time of the original distribution of landed property. The royal demesne could be increased, for example, as a result of forfeiture. Demesne lands were managed by stewards of the crown and were not given out in fief. During the reign of George III, Parliament appropriated the royal demesne, in exchange for a fixed annual sum, called the Civil List.

As common-law practice protected the rights of the villein, tenancy at the pleasure of the lord gradually developed into the added security of copyhold leases.

Since the demesne surrounded the principal seat of the lord, it came to be loosely used of any proprietary territory: ""the works of Shakespeare are this scholar's demesne." The "s" is not pronounced; if the word had survived into modern French it would have become "demêne." The less affected broad modern equivalent of "demesne" is "domain".