Under feudalism in France and England during the Middle Ages, tenure by serjeanty (/ˈsɑːrdʒənti/) was a form of tenure in return for a specified duty other than standard knight-service.

The word comes from the French noun sergent, itself from the Latin serviens, servientis, "serving", the present participle of the verb servo, "to keep, preserve, save, rescue, deliver". "Sergeant" is derived from the same source, though developing an entirely different meaning.

Serjeanty originated in the assignation of an estate in land on condition of the performance of a certain duty other than knight-service, usually the discharge of duties in the household of the king or a noble. It ranged from non-standard service in the king's army (distinguished only by equipment from that of the knight), to petty renders (for example the rendering of a quantity of basic food such as a goose) scarcely distinguishable from those of the rent-paying tenant or socager.

The legal historians Frederick Pollock and Frederic William Maitland (1895) described it as being a free "servantship" in the sense that the serjeant, whatever his task, was essentially a menial servant. However the feudal historian John Horace Round objected that their definition does not cover military serjeanties and glosses over the honorific value of at least some of the services.

The historian Mary Bateson stated as follows concerning serjeanties:

(They) were neither always military nor always agricultural, but might approach very closely the service of knights or the service of farmers ... The serjeanty of holding the king's head when he made a rough passage across the Channel, of pulling a rope when his vessel landed, of counting his chessmen on Christmas Day, of bringing fuel to his castle, of doing his carpentry, of finding his pot-herbs, of forging his irons for his ploughs, of tending his garden, of nursing the hounds gored and injured in the hunt, of serving as veterinary to his sick falcons, such and many others might be the ceremonial or menial services due from a given serjeanty.

The varieties of serjeanty were later increased by lawyers, who for the sake of convenience categorised under this head such duties as escort service to the Abbess of Barking, or of military service on the Welsh border by the men of Archenfield.

Serjeants (servientes) already appear as a distinct class in the Domesday Book of 1086, though not in all cases differentiated from the barons, who held by knight-service. A few mediaeval tenures by serjeanty can be definitely traced as far back as Domesday in the case of three Hampshire serjeanties: those of acting as king's marshal, of finding an archer for his service, and of keeping the gaol in Winchester Castle. It is probable, however, that many supposed tenures by serjeanty were not really such, although so described in returns, in inquisitions post mortem, and other records. The simplest legal test of the tenure was that serjeants, though liable to the feudal exactions of wardship, etc., were not liable to scutage; they made in place of this exaction special composition with the Crown.