"Measuring Polyphony" presents, for the first time, digitisations of polyphonic compositions copied in thirteenth- and fourteenth-century manuscripts in in mensural notation, and linked directly, where possible, to high-resolution images of the original manuscript sources, and MIDI audio files. The website offers new possibilities for mediating the scholarly and public experience of this richly evocative music within its original context. This project when the project director, Karen Desmond, was at the Schulich School of Music at McGill University, and now continues at Brandeis University. "Measuring Polyphony" leverages the potential of the rich digital image repositories of music manuscripts and the community-based standards for encoding music notation of the Music Encoding Initiative (MEI).