What happens to the meaning of authorship when a text appears anonymously? Such texts are certainly not authorless; the author has merely slipped behind a mask that makes his or her identity an open question for the reader. In the early modern period, anonymous publi­ cation was often no more than a temporary screening of authorship of contentious or otherwise controversial books. The secrecy afforded by anonymity might well be no more than an ephemeral feature of the text. Most scientific writing appeared in print firmly attached to the name, and often the portrait, of an author. There is, however, a small set of anonymous books on scientific subjects interesting for what they reveal about publication strategies, about the relation of authors to their readers, and more generally about the cultural context of scien­ tific knowledge in this period. Institutions and individuals, in fact, manipulated authorial invisibility for a variety of purposes.