Leiden University MS Lips 3 (2) contains a series of letters sent by the Brabant humanist Justus Lipsius (1547-1606) to his old university friend, the Jesuit Martin Delrio (1551-1608). They cover a crucial period in their relationship, from Lipsius’ return to the Catholic fold in Mainz in 1591 to his arrival in Leuven in 1593, his home for the remainder of his life. Lipsius’ letters were carefully copied and numbered by Delrio but subsequently edited by Lipsius. Closer study reveals that Lipsius seriously contemplated their publication. The fact that missing pages correspond with printed letters indicates that he physically excerpted them for publication. These insights, in turn, suggest that the material (manuscript) nature of Lipsius’ correspondence should not fool us: even when notionally private, his letters were always written with a potentially wider public in mind.