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The Bollandists are an association of scholars, philologists, and historians (originally all Jesuits, but now including non-Jesuits) who since the early seventeenth century have studied hagiography and the cult of the saints in Christianity. Their most important publication has been the Acta Sanctorum (The Lives of the Saints). They are named after Jean Bolland or Bollandus (1596–1665).
Acta Sanctorum 
The idea of the Acta Sanctorum was first conceived by the Dutch Jesuit Heribert Rosweyde (1569–1629), who was a lecturer at the Jesuit college of Douai. Rosweyde used his leisure time to collect information about the lives of the saints. 
Underestimating the magnitude of the undertaking, Bolland initially thought he could finish the work on his own, but after a few years he had to admit that the undertaking was beyond his individual strength. He was then assigned an assistant, Godfrey Henschen or Henschenius (1601–81). The first two volumes of the Acta, by Bolland and Henschen, were published in Antwerp in 1643.
Unlike Rosweyde and Bolland, Henschen was allowed to devote himself exclusively to the writing of the Acta. He solved many problems relating to chronology, geography and the philological interpretation of the sources. By the time of his death, 24 volumes had appeared; moreover, Henschen left many notes and commentaries for the following volumes. It can therefore be said that the Acta owe their final form to Henschen.
In 1659, Bolland and Henschen were joined by Daniel van Papenbroeck or Papebrochius (1628–1714), who devoted fifty-five years of his life to the Acta. From July 1660 until December 1662, Henschen and van Papenbroeck travelled through Germany, Italy and France in order to collect copies of hagiographic manuscripts. Another Bollandist of this period was Jean Gamans.
Suppression and relocation (18th century) 
When the Society of Jesus was suppressed by Pope Clement XIV in 1773, the Bollandists moved from Antwerp to Brussels, where they continued their work in the monastery of the Coudenberg until 1788, when the Bollandist Society was suppressed by the Austrian government of the Low Countries. Their library was acquired by the Premonstratensians of the Abbey of Tongerloo, who endeavored to carry on the work. The fifty-third volume was published by the abbot of Tongerloo in 1794. The 53 volumes of the first series covered the saints from January 1 to October 14.
After the re-establishment of the Society of Jesus in Belgium, a new Society of Bollandists was formed in the second quarter of the nineteenth century under the patronage of the Belgian government. The first volume of the new series appeared in 1845. A collection of 61 volumes was published in Paris between 1863 and 1867. By the end of the 19th century the work was re-oriented, bringing it more in line with the new philological methods. In 1882, a quarterly review on critical hagiography was established under the title of Analecta Bollandiana, which still exists today and publishes supplements to the Acta.
- Robert Godding, Bernard Joassart, Xavier Lequeux, François De Vriendt, Joseph van der Straeten, Bollandistes, saints et légendes. Quatre siècles de recherche hagiographique, Bruxelles, Société des Bollandistes, 2007. (French)
- Robert Godding, Bernard Joassart, Xavier Lequeux, François De Vriendt, De Rosweyde aux Acta Sanctorum. La recherche hagiographique des Bollandistes à travers quatre siècles, Bruxelles, Société des Bollandistes, 2009. (French, Italian and English)