A vassal or liege subject is a person regarded as having a mutual obligation to a lord or monarch, in the context of the feudal system in medieval Europe. While the subordinate party is called a vassal, the dominant party is called a suzerain. The rights and obligations of a vassal are called vassalage, while the rights and obligations of a suzerain are called suzerainty.
The obligations of a vassal often included military support by knights in exchange for certain privileges, usually including land held as a tenant or fief. The term is also applied to similar arrangements in other feudal societies.
In contrast, fealty (fidelitas) was sworn, unconditional loyalty to a monarch.
In fully developed vassalage, the lord and the vassal would take part in a commendation ceremony composed of two parts, the homage and the fealty, including the use of Christian sacraments to show its sacred importance. According to Eginhard's brief description, the commendatio made to Pippin the Younger in 757 by Tassilo III, Duke of Bavaria, involved the relics of Saints Denis, Rusticus, Éleuthère, Martin, and Germain – apparently assembled at Compiegne for the event. Such refinements were not included from the outset when it was time of crisis, war, hunger, etc. Under feudalism, those who were weakest needed the protection of the knights who owned the weapons and knew how to fight.
Feudal society was increasingly based on the concept of "lordship" (French seigneur), which was one of the distinguishing features of the Early Middle Ages and had evolved from times of Late Antiquity.
In the time of Charlemagne (ruled 768–814), the connection slowly developed between vassalage and the grant of land, the main form of wealth at that time. Contemporaneous social developments included agricultural "manorialism" and the social and legal structures labelled — but only since the 18th century — "feudalism". These developments proceeded at different rates in various regions. In Merovingian times (5th century to 752), monarchs would reward only the greatest and most trusted vassals with lands.