A Psalter is a volume containing the Book of Psalms and which often contains other devotional material. In the early Middle Ages Psalters were amongst the most popular types of manuscripts, rivaled only by the Gospel Books. Medieval Psalters often included canticles from the Old and New Testaments, as well as other devotional texts. Many Psalters were lavishly illuminated.
The psalter is also a part of either the Horologion or the breviary, both used to say the Liturgy of the Hours in the Eastern and Western Christian worlds, respectively.