 Here we are at the British Library in London, which holds one of the richest music collections in the world. The size and significance of this library has grown thanks to uniquely important donations and acquisitions, but also because of a system called legal deposit. Since its foundation in the 18th century, this institution has been entitled to receive a free copy of every new book, newspaper or music score published in the country, to be preserved for future generations. Legal deposit libraries are, among other things, extensive repositories of editions that were never used before reaching the library. Brand new items were, and still are, ideally placed to last as long as possible in the library's collection. In these titles, Fresh of the Press, one can expect to find few or no annotations, but the situation is different for materials that were previously used, those that were owned by individuals or other institutions, before being brought to this place of preservation. In such cases, markings of various kinds and other traces of usage are often present. Yet these traces are not always mentioned in the catalogue, in part because their essence is not easily captured. Unnotations can be of radically different kinds, from old shelf marks and personal notes to performance markings and added scripts, which we might struggle to read or understand. Similarly, the identity of people who left such annotations at various times from the 19th century until today often remains unknown to us. It is not surprising then that library catalogues focus on other information to identify items correctly. They distinguish, for instance, between this edition of Mozart music printed in London between 1800 and 1803, and its reprint from around 1820 when the publisher's name and address had changed. The catalogue generally organizes musical scores by telling the story of their production. In this case, the story is set in early 19th century London, only a few streets from here, where the Italian flutist and flute maker, Tebaldo Monzani, published and sold from his shop a lot of sheet music with flute or arranged for flute. In fact, Mozart had composed this particular piece as a trio for clarinet, viola and piano. Monzani, however, wanted to cater to people who played the flute, so he arranged Mozart's trio as a quartet for flute, violin, viola and cello. In a nutshell, the catalogue tells us how Monzani first published his arrangement while he was in business with another Italian, Giambattista Cimadoro, and later reissued it under a new partnership with Henry Hill. But production is not the whole story, and certainly not the only story these editions can tell. One copy arrived at the British Library just as Monzani produced it in the early 1800s. The edition is clean and his arrangement appears next to three other ones Monzani sold in the same collection. This other copy, however, is no longer simply what came out of Monzani's shop. Someone, we don't know who, purchased only this one arrangement, not the whole collection, and stitched it together with editions of other quartets by Mozart, Beethoven, Benincori, Pierrod and Philippe Mousart. Along with a custom binding, the owner prepared a new index for each of the four parts. These are significant annotations and traces of usage, telling a story about this person's taste in chamber music, including what else they would play alongside the Mozart-Monzani arrangement. We get a sense of someone in early 19th century London mixing up music sourced both locally and from elsewhere in Europe. We get also an idea of the system of knowledge which this person followed to organize music in their personal library. It is telling, in this respect, that no difference is made in the index between originals and arrangements, between music printed for string quartet and scores with a flute replacing the first violin, and that Beethoven appears alongside Mousart, a famously flamboyant conductor of prominent concerts. For the owner of this set of parts, such differences were not reasons to sort music into different categories. In this case, annotations don't just give us a picture of what happened to Mousart's music out in the world during the 19th century. They also provide us with a glimpse into the musical universe of the annotator, into how they made sense of the music they handled. Such glimpses can be revealing of conceptions and modes of handling music that were widespread in this period. For instance, the factor arrangements were held in more or less the same regard as original works. But they can also show more subjective attitudes, in the same year, even on the same day and in the same building, different individuals had different priorities when handling musical texts. Collecting autographed music manuscripts was common enough in this period, but those who did it were often pursuing different interests. The composer Luigi Kerubini exchanged some autographs in 1836 with a prominent Viennese collector, Alois Fuchs. Fuchs would attach to most of his autographs a separate page giving information about the author, their date of birth and death, their institutional appointments. In this case, Caldara's post at the Imperial Court in Vienna is mentioned, and details about the music contained in the manuscript. Here, it is specified that the manuscript is a cantata for voice and basto continuo. Once this item came into Kerubini's possession, however, it supported a different kind of intellectual pursuit. Kerubini was not interested in whether or not the autographs he collected were complete works, or whether the piece was a cantata or a symphony. His main preoccupation was collecting short autographs. If he got hold of longer ones, he would cut them down to size, so that he could place single pages written in the hands of different composers next to each other and compare their handwriting. To remember who was who during these comparative studies, he marked each page with the composer's surname, typically in red ink in the top left corner. So while Fuchs and Kerubini were both avid autograph collectors, they left different types of traces and annotations on their items, because collecting meant different things to them. Musicians can also provide a similarly nuanced perspective on the art of 19th century performers. They provide opportunities to learn about performer-specific attitudes with and around musical texts, and perhaps shed light on how musicians understood their own act of performance. In this respect, unnotated music can complement or even correct our understanding of performers based on with whom they studied or to which school of playing they belonged. This is an edition of Beethoven's violin concerto, heavily annotated in red crayon by Ferdinand David, the leader of the Leipzig Gewandhaus Orchestra. David was also a dedicated violin teacher and editor, and the level of detail in his unwritten markings show how he would often formalize a set of fingerings and bowings to be printed in a new edition, such as this one, where his name on the title page is bigger than that of Beethoven. This kind of edition, complete with ready-made fingerings by David, would then help less experienced violinists learn to play the piece. But many other 19th century performers and teachers did not share David's calling to make music more widely accessible in this manner. The violinists and Paris Conservatoire professor Pierre Bayot left behind a richly unnotated library, but this was mostly for his own and his ensemble's use. There seems to have been no motivation on his part to formalize sets of performance indications for a wider public. David was also someone who, when rehearsing string quartet, would often reach over his colleagues' shoulders to write fingerings directly into their parts. Concertmaster habits are hard to break. While Bayot was equally passionate about playing quartets, he appears not to have worked in this way with his ensemble. So the parts are notated by these two violinists, capture elements of their differing rehearsal habits, which we otherwise would not know about, as written descriptions of what they did to prepare for concerts are scant at best. This is a kind of knowledge that is not usually gained in reading published manuals from the period on how to play the violin. Annotations may be scattered in the margins of 19th century music editions and manuscripts, but they don't deserve to remain in the margins of discussions about music and musical culture of the time. They can enrich our understanding of the many and multifaceted ways in which people interact with music and with each other while handling musical artifacts.