In recent times discoveries of previously unknown medieval manuscripts of great beauty or historic importance have become rare events, which appear all the more remarkable if the discovery is made in a totally unexpected place. Felix Heinzer's identification of a psalter of the Bohun family in the archives of the active Cistercian convent of Lichtenthal in the German state of Baden is one such find. The Bohun family rose to prominence in England in the course of the thirteenth century. Hereditary Constables of England, by 1361 the Bohuns, as earls of Hereford, Essex and Northampton, were holders of vast estates across the breadth of the land. They became one of the most important patrons of 14th-century manuscript production in England. The present study of this fully-illustrated psalter reproduces every illumination in full-color and original size, with many black and white details and comparative illustrations. A detailed description of each illuminated folio is included. The author also provides a complete historical background of the Bohun family.