The Liber instrumentorum vicecomitalium (Latin for "Book of the Instruments of the Viscounts"), sometimes called the Trencavel Cartulary (CT) or Cartulaire de Foix, is a high medieval cartulary commissioned by the Trencavel family. It preserves either 585 or 616–7 charters, the earliest of which dates to 1028 and the latest to 1214. The charters preserve a record of important feudal customs relating to the lands of the Trencavel, namely , , Béziers, Carcassonne, , and , all of which—save Carcassonne, which was a county—were viscounties, hence the cartulary's name. It is preserved in a twelfth-century manuscript, now kept with the Société Archéologique de Montpellier, where it is MS 10.