Martín Antonio del Río or Martin Antoine del Rio (17 May 1551, Antwerpen – 19 October 1608, Leuven) was a Jesuittheologian of Spanish descent. He was born in Antwerp, and studied at numerous institutions, receiving the degree of Doctor of Law from Salamanca in 1574. After a period of political service, he became a Jesuit in 1580. He taught theology for several years in Leuven, Mainz, and Douai; all intellectual centres for the Catholic Reformation.
He wrote, among other books, Disquisitionum magicarum libri sex, a work on magic and the occult. This work, first published in three parts over 1599 to 1600, was reprinted at least 20 times, making it the second most popular book, after Malleus Maleficarum, on the occult. It was last reprinted in 1755 in Cologne. In the Disquisitionum, Delrio made a connection between witches and heretics. The book was popular amongst both Catholics and Protestants, and was one of the books used at the famous Salem witch trials of 1692.
His friend the Flemish humanist Justus Lipsius called him "the wonder of the century". Posterity, however, has not been so generous. For Voltaire he was the “procureur general de Beelzebuth”. For the nineteenth century authors of the Biographie Nationale de Belgique, an anthology of short biographies, Del Rio was something of an embarrassment. Some modern historians, most notably Robert Muchembled, have accused him of being the principal cause of witch-hunts in the Southern Netherlands. Most historians, however, have noticed Delrio's relative moderation on the subject of witchcraft.