The Modena Codex (Modena, Biblioteca Estense, α.m.5,24; often referred to with the siglum Mod A) is an early fifteenth-century Italian manuscript of medieval music. The manuscript is one of the most important sources of the ars subtilior style of music. It is held in the Biblioteca Estense library in Modena.
The precise origin of Mod A is controversial, with Pavia/Milan, Pisa and Bologna all being proposed. Firm evidence of ownership of the book by the Biblioteca Estense only occurs in the early nineteenth century, although a 1495 catalogue of the Este family library in Ferrara might refer to it. It was rediscovered by the philologist Antonio Cappelli in 1868.
