John XVIII (or XIX) (born, Rome—died June/July 1009, Rome) was the pope from 1003 to 1009.
Like his predecessor, Pope John XVII, his election was influenced by the Roman patrician John Crescentius III. More independent of the powerful Italian Crescentii family than John XVII, he eventually abdicated for unknown reasons and died shortly thereafter at the monastery of St. Paul Outside the Walls, Rome.