The Lexicon musicum Latinum (LmL), begun in 1961, aims to comprehend and investigate the language special to a particular discipline: medieval Latin writing on music. The undertaking should culminate in the publication of a dictionary which makes accessible Latin musical terminology on a scholarly basis. Set down in numerous medieval texts, theoretical discussions of music are of quite special significance for modern study, for they are an important means of understanding music which is completely foreign to us. Only when such a lexicon is available will it be possible to put on a scientifically established basis our pursuit of the tradition of medieval music, which occupies a crucially important position at the beginning of western music.