The Book of Psalms (Bible) has been, no doubt, the single most important source of text in music history. The psalms are by far the most important texts used in Gregorian chant. In the early days of Christian worship the service consisted only of psalm singing, and in spite of the many fundamental changes that took place in ensuing centuries the psalms retained their dominant position in the Roman liturgy.

Development, which may have taken place between the years 400 and 800, led to a variety of forms and types for the different items of the chant, each item receiving the structure proper to it from the standpoint of the liturgy. All these forms stem from three original types:

(1) direct psalmody, in which the psalm is sung with no refrain by a soloist or a choir

(2) responsorial psalmody, in which a soloist sings the verse and is answered by a choir

(3) antiphonal psalmody, in which the choir is divided into two groups singing alternately