Under the system of feudalism, a fiefdom, fief, feud or fee, consisted of heritable lands or revenue-producing property granted by a liege lord in return for a vassal knight's service (usually fealty, military service, and security). It usually required the vassal to obey conditions of customary and specified homage and fealty. In theory, a fief would provide revenue to equip and support the vassal knight to serve the liege lord. The fief was granted but remained in the ownership of the liege lord. The lord did not have the right to withdraw the fief (unless the vassal broke his obligation) or to increase the dues for a fief.

Fiefs division could occur in a unlimited fashion, known as subinfeudation. This tended to weakening the unifying strength of the fief system due to exaggerated distributed power structure and reduced efficiency in the feudal system.

The simplest form of a fief existed as a self-sufficient estate.

Fiefs, typically 1000 to 2000+ acres (4 to 8 km&sup2), consisted of housing structures, barns, and gardens. There usually was a hall (not necessarily a manor), religious structures (commonly a church), a mill, a winery, and / or an oil press on the fief. The fief commonly had arable land, meadows, pastures (the commons), fishponds, and forests. Fiefs that possessed cultivated arable land were divided into three large fields and farmed by the three-field system of agriculture. One field was devoted to winter crops, another to summer crops, and a third lying fallow each year. The land was worked by peasants (known as serfs). Generally, rights of cultivation on the fief were heritable among the serfs

The vassal knight occupied the lord's fortified dwelling known as the manor house (if there was such a structure existing). Larger-than-common fiefs were in the hands of a vassals-in-chief. Although a fief was usually a piece of land, it could also take the form of money or food called a Knight's fee.

Fief lands eventually gave way to the village concept towards the end of the medieval age.

In Japan, fiefs are called "han."