Purgatorial societies are Roman Catholic Church associations or confraternities which aim to assist souls in purgatory reach heaven. The doctrine concerning purgatory (the term for the intermediate state in Roman Catholicism), the condition of the poor souls after death (particular judgment), the communion of saints, and the satisfactory value of our good works form the basis of these associations.

In the present day, many purgatorial societies exist, such as the Purgatorian Archconfraternity, which is run by the monks in the religious order of Transalpine Redemptorists; the Central Ohio Purgatorial Society, a lay apostolate; Saint Gertrude Purgatorian Society, which is based in the United States; the Guild of All Souls, which is a traditionalist Catholic purgatorial society under the auspices of the Guild of St. Peter ad Vincula; and the Holy Souls Registry, that is run by America Needs Fatima.

For centuries, associations praying for the purgatorial souls were common. The old religious orders, e.g. the Benedictine Order, especially the Order of Cluny which inaugurated All Souls' Day, also met some of this need. Religious confraternities are likewise distinguished in their early beginnings by a special devotion to the sick and burial of the deceased (e.g. the brotherhood of Constantinople which flourished in 336, and in the West the Confratriæ or Confraternitates of the Middle Ages). Even medieval guilds, established primarily for secular purposes, included in their constitutions to require charity for deceased members.

In Northern Europe, the medieval associations of prayer called "fraternitates", "societates", and "consortium" are not as well known, although some "Totenbünde" (German for associations for the dead) existed, affording one of the best proofs of the existence of lively faith, especially among the Anglo-Saxons, Franks and the Germanic peoples in general. They were founded chiefly, though not solely, to assist deceased members with prayers, Mass and works of Christian charity.

Ducange-Favre defines a Confraternitas "as ... a society formed between various churches and monasteries, abbeys, bishops and noblemen; later kings, princes, bishops, priests and the laity, especially ecclesiastical benefactors, were admitted". The admission papers or the constitutions of the brotherhood usually stated in detail how many Masses, what prayers, and good works would be offered on their death for the repose of the souls of deceased members, in the place of worship or by individuals. The members were enrolled in a registry (a Liber Vitæ or 'book of life'), a development of the ancient diptychs. Upon the death of a member, a messenger was immediately dispatched with a circular (rotulus) to announce the death to all the affiliated monasteries, where the name was inserted in list of the dead. These lists of the dead were also known as necrologies for constant commemoration; these lists were, like the earlier diptychs, read aloud so that special prayers might be said for the deceased mentioned, and a special commemoration made by the priest during the Eucharist.

In the West, these confraternities attained their greatest prosperity during the era from Carolingian reigns till the end of feudalism. In c. 1400 England, Wyclif issued the first public opposition to these associations. These brotherhoods may be divided into those formed of several monasteries or churches, or individual bishops, priests, abbots and monks. However, kings, princes and other laymen, especially benefactors, were admitted into these three classes, and even the frequently very numerous subordinates of a monastery.

Especially during their peak, confraternities were formed among monasteries. In the 9th century, Reichenau was affiliated with more than a hundred other monasteries and chapters in Germany, Switzerland, France and Italy. This affiliation was chiefly due to the reform of the monastery by St. Benedict of Aniane, and is the largest brotherhood known to us. Alcuin worked in the west of the Frankish Empire, and before him St. Boniface had sought with eager zeal to establish and foster in Germany such unions and brotherhoods with England and Italy. Similarly an "Act of Spiritual Association" between the Abbeys of St. Denis of France and St. Remy of Reims arranged that, within thirty days after the death of a member, the entire Office be recited by each of the surviving members, that the priests say Masses corresponding to the various offices, and that vigils be held in common on the first, seventh, and thirteenth days. At mediaeval synods, the bishops and abbots present frequently formed themselves into such brotherhoods, often extending to the cathedral chapters and monasteries, and to the kings and princes who were present at the councils – in the 8th and 9th centuries, a series of such synods took place: Attigny (762); Dingolfing (769); Frankfort (794); Salzburg (799); Freising (805); Clechyt 815; Savionières near Toul (850). Brotherhoods were also formed at other English and Italian synods. At diocesan synods all the clergy of a diocese with their bishop formed themselves into brotherhoods, and frequently priests of still smaller districts (rural chapters) formed lesser associations of prayer to which the laity were also admitted. Individuals of every station, rank, and sex eagerly joined these associations, while numerous rich persons funded monasteries to insure a special share in their suffrage after death. English kings, bishops, abbots and Carolingian kings gave them an excellent example, as did St. Boniface and Alcuin. Even the laity of the lower classes joined the brotherhoods of St. Gall and Reichenau. The communion of spiritual goods and indulgences, granted by monasteries in the last centuries to another monastery, to benefactors and friends outside the cloister, or to other confraternities, is more than a memorial of the old brotherhoods, since in these grants (communicationes) the promise of spiritual help for the deceased is one of the chief features.

Along with these brotherhoods, there appeared Confraternitaties more closely resembling the present associations. Their chief object was care for the poor souls. Among these might be included the associations devoting themselves to the spiritual welfare of the dying and their burial. Of the confraternities of the dead, only examples can be cited from the earlier centuries, but these show sufficiently clearly how widespread these must then have been. According to an inscription in the Church of Ss. Cosmas & Damian in Rome a number of priests and bishops in Rome formed themselves into an association of sodales (c. 985), each promising that on the death of a member he would immediately sing forty Masses for the repose of his soul.