Jacobus of Liège (died after 1330) was a music theorist active in the Southern Netherlands in the late middle ages.
A contemporary treatise, written not long after 1376, mentions a certain Jacobus de Montibus as an expert on the genera of ancient Greek music theory.
A canon named Jacobus de Montibus was resident in the church of Saint Paul (now cathedral) in Liège during the 1320s and 1330s.
[5] Further research demonstrated that Ispania more likely refers to Hesbaye, an archdeaconate in the diocese of Liège known in Latin as Hispania or Hesbania.
[6] Of the seven books of Speculum musicae, the last has received the most attention for its long argument against unnamed "moderni" (including Philippe de Vitry and Johannes de Muris), whom Jacobus held responsible for corrupting the mensural notation system as defined by Franco of Cologne.