In 1892 Fr Delehaye was appointed by his Jesuit superiors to be a fellow of the Society of Bollandists, named for the 17th-century hagiographical scholar Jean Bolland, S.J., and founded the early seventeenth century specifically to study hagiography, research towards the gathering and evaluation of historical documentary sources regarding the life and cult of Christian Saints.

[1] In the earlier part of the twentieth century fears arose in the Catholic Church about the theological consequences of some methods used in critical historical studies, including biblical scholarship.

[6] As part of the controls put in place by the Catholic authorities, the Bollandists' scholarly journal Analecta Bollandiana, was subject to censorship by the Holy Office during the years 1901–1927.

These were issues of broader scope that did not prevent Fr Delehaye from continuing as a priest in good standing to pursue his researches with the Bollandists for the greater part of his long life and maintaining his international reputation as a respected and able scholar.

[1] Delehaye's major publications, works of method and synthesis that are of general use to historians, are: Other important works, with more restricted focus, are: Posthumous collections of fugitive pieces were published in 1966 as Mélanges d'hagiographie grecque et latine and in 1991 as L'ancienne hagiographie byzantine: les sources, les premiers modèles, la formation des genres, the previously unpublished texts of lectures delivered in 1935.