Lucien or Lucianus Ceyssens OFM (1902–2001) was a twentieth-century ecclesiastical historian who specialised in the history of Jansenism.
In 1921 he entered the Order of St Francis, and in 1927 he was ordained priest.
[1] From 1934 to 1963 he taught at the Pontifical University Antonianum in Rome, except during the years of the Second World War (1940–1945), when he was in Belgium.
As a historian, he had a marked impact on the modern understanding of the seventeenth-century religious controversies between Jansenists and anti-Jansenists.
[3] In 1963 a Festschrift was published to mark his 60th birthday, Miscellanea Jansenistica offerts à Lucien Ceyssens, O.F.M., and in 1992 a collection of his own articles was published as Le Sort de la bulle Unigenitus to mark his 90th birthday.