The Old Hall Manuscript, the most important record of early harmony in England, and one of the oldest surviving collections of English part music, was compiled by a single scribe between about 1415 and 1421. It may have originated in the private chapel of Thomas of Lancaster, 1st Duke of Clarence, the second son of King Henry IV. Written in large format, 41 x 26 cm, it was intended to be readable from a distance by a choir.
It "is made up mostly of settings of the Ordinary of the Mass, together with some antiphons and motets. The majority of the music has not survived elsewhere. The book is of incomparable value because it shows us an English repertory for which the names of individuals are given for the first time.
"The manuscript identifies numerous English composers, including one 'Roy Henry', who is most likely to have been Henry V. Two of the motets may be associated with the Battle of Agincourt (1415) and another is one of the most celebrated works by John Dunstable (died 1453) whose music is considered to incarnate the spirit of the Renaissance in England.
"The volume is arranged by sections devoted to particular parts of the Ordinary of the Mass, so that different settings of the Gloria, Sanctus, and so on are grouped together. Some are written in score, others in parts. The manuscript takes its name from a previous owner, St Edmund's College, Old Hall Green, Ware, in Hertfordshire" (http://www.bl.uk/onlinegallery/onlineex/musicmanu/oldhall/, accessed 11-06-2013).
The manuscript (British Library, Additional MS 57950) was acquired by the British Library in 1973. A digital facsimile may be available from the Digital Archive of Medieval Music.