What did it mean for Guillaume Du Fay (ca. 1397-1474), chameleon-like expert in every musical genre of his day, to compose four settings of the Mass Ordinary toward the end of his life? Looking back from the vantage point of the next generation, when the polyphonic mass reigned supreme, it might be tempting to interpret these works as a self-conscious summa of Du Fay’s career – an achievement akin to Haydn’s London Symphonies or Beethoven’s late string quartets. On a purely musical level these comparisons are apt. Each mass stakes out unique musical terrain; they are often strikingly experimental; and the entire set is shimmeringly beautiful from beginning to end, revealing a composer at the height of his powers.