This collection of sacred music was compiled by a single scribe between about 1415 and 1421.
In the early 1420s additional leaves were inserted by other writers, resulting in a repertory which is now the most important source for our knowledge of early harmony music in England.
The manuscript is made up mostly of settings of the Ordinary of the Mass and is arranged in sections so that different setting of the Gloria, Sanctus and so on, are grouped together. The notation is extremely precise and complex, suggesting a high degree of sophistication in the writer and intended users of the book, as well as the composers.
The manuscript identifies a number of the composers, including one 'Roy Henry', who is most likely to have been Henry V. Two of the motets, or choral compositions, may be associated with the Battle of Agincourt.
The manuscript takes its name from a previous owner: St Edmund's College, Old Hall Green, Ware, in Hertfordshire.