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).

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. On his death, Bolland continued his work in Antwerp.

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.