An oath of fealty, from the Latin fidelitas or faithfulness, is a pledge of allegiance of one person to another. Typically the oath is made upon a religious object such as a Bible or saint's relic thus binding the oath taker before God.

In medieval Europe, fealty was sworn between two people, the obliged person (vassal) and a person of rank (lord). This was done as part of a formal commendation ceremony to create a feudal relationship.

Fealty and homage are a key element of feudalism.

The term is also used by English speakers to refer to similar oaths of allegiance in other feudal cultures, as with Japan prior to about 1500.

See also: homage, feudalism, vassal, commendation ceremony