This article provides the first ever study of the complex genesis of Eckhel's Doctrina numorum veterum. A key aspect of the contribution is the presentation of rediscovered numismatic papers of the Danish archaeologist Georg Zoëga at the Royal Library in Copenhagen: these manuscripts could be identified as the notes that Zoëga took while studying numismatics in Vienna with Eckhel in 1782. Since we know that Zoëga directly copied Eckhel’s manuscripts, they represent a most precious (because precisely dated) source for the progress Eckhel had made with his work up to 1782. Further aspects of the contribution concern Eckhel’s scholarly practice: an analysis of Eckhel’s various notebooks and preparatory manuscripts for the Doctrina (and other works) kept in Vienna allows for a look over the author’s shoulder while he was penning his works. One of the results of this study is that only very few quires of the final manuscript from which the Doctrina was typeset are preserved, and that the vast majority of the Doctrina-related manuscripts that have come down to us belong to earlier phases of the work’s redaction. In one of these phases, the section on Greek coins was headlined Geographia numaria – a title that does not appear in the Doctrina.