Digital editions have grown considerably in importance in the last two decades. This also applies to the electronic edition of music-theoretical writings, which were part of this process from the early nineties through many seminal projects focused on Latin, Italian, English, French and Spanish sources. Due to its theoretical, linguistic but also typographical complexity, the German corpus, however, has acquired a particular status in this process. The VD16 and VD17 digitization projects carried out in Germany have dramatically improved the access to these sources. However, despite their crucial historical importance, no systematic musicological investigation of these writings has been undertaken with the tools of digital humanities so far. The project Thesaurus Musicarum Germanicarum (TMG), jointly initiated at the University Paris-Sorbonne and Humboldt University, Berlin, aims to fill this gap through a multidisciplinary approach, bringing together librarians, researchers in digital humanities, and musicologists. The project has three main goals: 1) providing full text access to the sources through critical electronic editions; 2) creating tools for investigating intertextual relationships; and 3) contributing to a systematic study of the source’s music-theoretical contents through a thesaurus. First, this talk will describe the different levels of collaboration between libraries, centres for digital humanities and research institutes in musicology. The presentation will focus on the transcription methods used, and the way the XTF framework (Californian Digital Library) has been implemented to meet the specific project’s requirements. This section will also explain how the libraries and cultural institutions contribute to the project with their specific expertise in databases and electronic edition. Second, the project’s methodology will be described through examples illustrating how the XML-TEI/MEI markup language is used to grasp the three dimensions of the source (text, illustrations, and musical examples) and then to combine the original contents with a modern edition. Our presentation will then show the critical apparatus, indices and maps, which contribute to the identification of the cultural, intellectual, geographical and historical contexts. Finally, we will present statistical tools used for creating semantic networks and a thesaurus, which gathers definitions of musical terms. Our talk will conclude with a general reflection on the benefits and limits of digital humanities applied to the editing and investigation of music-theoretical writings.