The eleventh fascicle of W1 (Herzog August Bibliothek, 628 Helmst.) has been recognized as a “monument” of polyphony in the British Isles, and the only complete collection of polyphony from the British Isles between the Winchester Troper and the Old Hall Manuscript. Despite these assertions, the eleventh fascicle has not been considered for what is it - a collection of two-part pieces for the daily Lady mass. This seminar addresses the context of W1 in developing tradition of the daily Lady mass in the British Isles, one of the most important occassions for liturgical polyphony in the thiteenth and fourteenth centuries. W1, along with a handful of other sources, indicate that by the mid-thirteenth century, the Lady mass celebrated the Lady of Heaven with music that made every day a feast in the Lady chapel. The compiler and editor of eleventh fascicle of W1, who was also responsible for copying the fascicles of W1 that contain the famous Notre Dame polyphony, drew from Notre Dame polyphony and English devotions that viewed the Life of Christ through a Marian lens to provide daily rotation of polyphony for the Lady mass at St Andrews Cathedral.