Besides printers and engravers, copyists are essential links in the production of musical sources. They may work in a very productive workshop (Philidor and Fossard's is a typical example), or alternatively they may be occasional copyists, in charge of preparing the performance of a particular work. Their production can be part of a commercial aim (as at Foucault and Loulié) or a heritage ambition. Their production has been considered mainly through studies of music collections or in the study of a composer's critical edition. Their work is all the more difficult to appreciate because their copies are rarely signed nor dated, so that their identification is sometimes difficult. In addition to the handwriting itself, their work can be qualified with the tools of codicology (papers, collation, binding...) as well as rastrology (layout, measurements, inks...).