Abbot is an ecclesiastical title given to the head of an independent monastery for men in various Western Christian traditions. The name is derived from abba, the Aramaic form of the Hebrew ab, and means "father". The female equivalent is abbess.

The title had its origin in the monasteries of Egypt and Syria, spread through the eastern Mediterranean, and soon became accepted generally in all languages as the designation of the head of a monastery. The word is derived from the Aramaic av meaning "father" or abba, meaning "my father" (it still has this meaning in contemporary Arabic: أب, Hebrew: אבא and Aramaic: ܐܒܐ) In the Septuagint, it was written as "abbas". At first it was employed as a respectful title for any monk, but it was soon restricted by canon law to certain priestly superiors. At times it was applied to various priests, e.g. at the court of the Frankish monarchy the Abbas palatinus ("of the palace"') and Abbas castrensis ("of the camp") were chaplains to the Merovingian and Carolingian sovereigns' court and army respectively. The title of abbot came into fairly general use in western monastic orders whose members include priests.

An abbot (from Old English: abbod, abbad, from Latin: abbas ("father"), from Ancient Greek: ἀββᾶς (abbas), from Imperial Aramaic: אבא/ܐܒܐ ('abbā, "father"); compare German: Abt; French: abbé) is the head and chief governor of a community of monks, called also in the East hegumen or archimandrite. The English version for a female monastic head is abbess.

In Egypt, the first home of monasticism, the jurisdiction of the abbot, or archimandrite, was but loosely defined. Sometimes he ruled over only one community, sometimes over several, each of which had its own abbot as well. Saint John Cassian speaks of an abbot of the Thebaid who had 500 monks under him. By the Rule of St Benedict, which, until the Cluniac reforms, was the norm in the West, the abbot has jurisdiction over only one community. The rule, as was inevitable, was subject to frequent violations; but it was not until the foundation of the Cluniac Order that the idea of a supreme abbot, exercising jurisdiction over all the houses of an order, was definitely recognised.

Monks, as a rule, were laymen, nor at the outset was the abbot any exception. For the reception of the sacraments, and for other religious offices, the abbot and his monks were commanded to attend the nearest church. This rule proved inconvenient when a monastery was situated in a desert or at a distance from a city, and necessity compelled the ordination of some monks. This innovation was not introduced without a struggle, ecclesiastical dignity being regarded as inconsistent with the higher spiritual life, but, before the close of the 5th century, at least in the East, abbots seem almost universally to have become deacons, if not priests. The change spread more slowly in the West, where the office of abbot was commonly filled by laymen till the end of the 7th century. The ecclesiastical leadership exercised by abbots despite their frequent lay status is proved by their attendance and votes at ecclesiastical councils. Thus at the first Council of Constantinople, AD 448, 23 archimandrites or abbots sign, with 30 bishops.

The second Council of Nicaea, AD 787, recognized the right of abbots to ordain their monks to the inferior orders below the diaconate, a power usually reserved to bishops.

Abbots used to be subject to episcopal jurisdiction, and continued generally so, in fact, in the West till the 11th century. The Code of Justinian (lib. i. tit. iii. de Ep. leg. xl.) expressly subordinates the abbot to episcopal oversight. The first case recorded of the partial exemption of an abbot from episcopal control is that of Faustus, abbot of Lerins, at the council of Arles, AD 456; but the exorbitant claims and exactions of bishops, to which this repugnance to episcopal control is to be traced, far more than to the arrogance of abbots, rendered it increasingly frequent, and, in the 6th century, the practice of exempting religious houses partly or altogether from episcopal control, and making them responsible to the pope alone, received an impulse from Pope Gregory the Great. These exceptions, introduced with a good object, had grown into a widespread evil by the 12th century, virtually creating an imperium in imperio, and depriving the bishop of all authority over the chief centres of influence in his diocese.

In the 12th century, the abbots of Fulda claimed precedence of the archbishop of Cologne. Abbots more and more assumed almost episcopal state, and in defiance of the prohibition of early councils and the protests of St Bernard and others, adopted the episcopal insignia of mitre, ring, gloves and sandals.