This article presents the letters written by the composer Orlandus Lassus(1532-1594) to duke William V of Bavaria (1548-1626). The correspondenceconsists of two very different groups of letters: on the one hand autographswhich are clearly situated in a very personal and intimate sphere ofcommunication, on the other hand printed dedication letters showing all theexpected rhetorical formality. The comparison between the two sorts of letters,which can also be read as an introduction to the correspondence of Lassus,shows the difference, especially on a linguistic level, between private and publiccommunication.