From The Art and Popular Culture Encyclopedia
An abbess (Latin abbatissa, fem. form of abbas, abbot) is the female superior, or Mother Superior, of an abbey of nuns. An Abbess is the female version of an Abbot. In Roman Catholic and Anglican abbeys, the mode of election, position, rights, and authority of an abbess correspond generally with those of an abbot. The office is elective, the choice being by the secret votes of the sisters from their own body. Like the abbot, the abbess is solemnly admitted to her office by formal blessing, conferred by the bishop in whose territory the monastery is or by an abbot or another bishop with his permission. Unlike the abbot, she receives only the ring and a copy of the rule of the order: the abbess does not receive the mitre, and she is not given a crosier as part of the blessing ceremony though, by ancient tradition, she may carry one when leading her sisters. She also traditionally adds a pectoral cross to her habit as a symbol of office.
Abbesses are, like abbots, major superiors in canon law. They receive the vows of the sisters of the abbey and have full authority in its administration. As they do not receive Holy Orders, in the Roman Catholic Church they do not have many of the other powers conferred upon abbots, however, and they do not exercise authority over territories outside of their monastery.
Historically, in some Celtic monasteries abbesses presided over joint-houses of monks and nuns, the most famous example being St. Brigid's leadership in the founding of the monastery at Kildare. This custom accompanied Celtic monastic missions to France and Spain, and even to Rome itself. At a later period, in 1115, Robert, the founder of Fontevraud Abbey near Chinon and Saumur, France, committed the government of the whole order, men as well as women, to a female superior.
In the Lutheran Church the title of abbess (Äbtissin) has in some cases — e.g. Itzehoe — survived to designate the heads of abbeys which since the Protestant Reformation haves continued as Stifte, i.e. collegiate foundations, which provide a home and an income for unmarried ladies, generally of noble birth, called canonesses (Kanonissinen) or more usually Stiftsdamen. This office of abbess is of considerable social dignity, and was sometimes filled by princesses of the reigning houses. Until the dissolution of Holy Roman Empire and mediatization of smaller imperial fiefs by Napoleon, the evangelical Abbess of Quedlinburg was also per officio the head of that reichsunmittelbar state. The last such ruling abbess was Sofia Albertina, Princess of Sweden.