There are numerous references to psalms in the General Instruction of the Roman Missal. Presented here is the main paragraph on the Responsorial Psalm.
Other paragraphs related to psalms include paragraphs #37 (Responsorial Psalm an independent rite), #39 (importance of singing Responsorial Psalm), #43 (posture during the singing of the Responsorial Psalm), #48 (use of psalms for Entrance song), #57 (not lawful to replace Responsorial Psalm with non-Biblical texts), #62 (use of psalms instead of Alleluia during Lent), #63 (use of psalms when only one reading before the Gospel), #87 (use of psalms during communion procession), #88 (use of psalms of praise after communion), #99 (lector reciting psalms if no psalmist), #102 (ministry of psalmist), #309 (The Ambo is the preferred place for singing the Responsorial Psalm, #352 (Collaboration of ministers in planning the selection of texts for Mass, including the text for the Responsorial Psalm), #391 (Approval of translations for psalm texts).
The Responsorial Psalm
61. After the First Reading follows the Responsorial Psalm, which is an integral part of the Liturgy of the Word and which has great liturgical and pastoral
importance, since it fosters meditation on the Word of God.
The Responsorial Psalm should correspond to each reading and should usually be taken from the Lectionary.
It is preferable for the Responsorial Psalm to be sung, at least as far as the people’s response is concerned. Hence the psalmist, or cantor of the Psalm,
sings the Psalm verses at the ambo or another suitable place, while the whole congregation sits and listens, normally taking part by means of the response,
except when the Psalm is sung straight through, that is, without a response. However, in order that the people may be able to sing the Psalm response
more easily, texts of some responses and Psalms have been chosen for the different times of the year or for the different categories of Saints. These may be used instead of the text
corresponding to the reading whenever the Psalm is sung. If the Psalm cannot be sung, then it should be recited in a way that is particularly suited
to fostering meditation on the Word of God.
Instead of the Psalm assigned in the Lectionary, there may be sung either the Responsorial Gradual from the Graduale Romanum, or the Responsorial Psalm
or the Alleluia Psalm from the Graduale Simplex, as described in these books."