Any account of music books in Britain in the later Middle Ages is of necessity hampered in two major respects. The widespread destruction of books at the time of the Reformation was inevitably meted out with particular vigour to books of plainchant and other Latin liturgical music, to the extent that only a very small number of these fundamental musical sources remains intact, out of the many thousands that must once have existed. Conversely, instrumental music was only very exceptionally notated in this period: no more than a few fragments survive today, but they are not likely to bear witness to a widespread practice of writing down this music. Similarly, the written sources of secular song are far fewer than are found in other countries, or from later centuries in Britain. This is not to say that secular music held a less important place in cultural life, merely that it was not so dependent on the written record. We know that some of the courtly songs of the troubadours were sung in England, but no English books comparable with the luxurious French chansonniers are extant. What music manuscripts do survive, though, make it abundantly clear that the British Isles were far from being a musical backwater: some of the most technically complex polyphonic liturgical music to survive from the thirteenth and fourteenth centuries anywhere is known from British sources, and there are many innovations in other branches of music from the time. Moreover, several notable English writers brought new levels of understanding to the theory of music.