Lucas Holstenius, born Lukas Holste (1596 – February 2, 1661), was a German Catholic humanist, geographer and historian.
Born at Hamburg in 1596, he studied at the gymnasium of Hamburg, and later at Leyden University, where he was closely acquainted with some of the most famous scholars of the age, including Johannes Meursius, Daniel Heinsius and Philip Cluverius, whom in 1618 he accompanied on his travels in Italy and Sicily, thus giving him a taste for the study of geography. Disappointed at his failure on his return to obtain a post in the gymnasium of his native Hamburg, he left Germany for good. Having spent two years from 1622 in England, at Oxford and London, gathering materials for his Geographi Minores, he then proceeded to Paris.
At Paris in 1624, he became librarian to the President de Mesmes, the friend of the scholarly brothers Dupuy, and the correspondent of N. Peiresc. At this time he was converted to Catholicism. It seems that it was the liking he had always displayed for Platonic philosophy impelled him to read eagerly the Greek and Latin Fathers, especially those who treated of contemplative and mystical theology that led him to this step.
In 1627 he went to Rome, and through the influence of Peiresc was admitted to the household of Cardinal Francesco Barberini, former papal nuncio and the possessor of the most important private library in Rome. In 1636 he became the cardinal's librarian.
Finally, under Innocent X, he was placed over the Vatican Library. The popes sent him on various honorable missions, such as bearing the cardinal's hat to the nuncio at Warsaw in 1629, and Alexander VII sent him to Innsbruck to receive abjuration of Protestantism by Christina, former Queen of Sweden. He also acted as intermediary in the conversion of the Danish nobleman, the Landgrave of Darmstadt and of Ranzau.