Acta Sanctorum (Acts of the Saints) is an encyclopedic text in 68 folio volumes of documents examining the lives of Christian saints, in essence a critical hagiography, which is organised according to each saint's feast day. The project was conceived and begun by Jesuit monk Heribert Rosweyde. After his death in 1629, the Jesuit scholar Jean Bolland ('Bollandus', 1596–1665) continued the work, which was gradually finished over the centuries by the Bollandists, who continue to edit and publish the Acta Sanctorum.
The Acta Sanctorum began with two January volumes (for saints whose feast days were in January), published in 1643. From 1643 to 1794, 53 folio volumes of Acta Sanctorum had been published, covering the saints from January 1 to October 14. The main work ended with the Propylaeum to December published in 1940. The Bollandists oversaw the project, first in Antwerp and then in Brussels. After the creation of the Kingdom of Belgium, the Bollandists were permitted to reassemble, working from the Royal Library of Belgium in Brussels. When the Jesuits were suppressed by the Habsburg governor of the Low Countries in 1788, the Bollandists continued their work in the Tongerlo Abbey.
In addition to the extraordinary amount of biographical material, extensively researched, the Acta Sanctorum broke new ground in its use of historical criticism.