After the reading that immediately precedes the Gospel, the Alleluia or another chant indicated by the rubrics is sung, as required by the liturgical season. An acclamation of this kind constitutes a rite or act in itself, by which the assembly of the faithful welcomes and greets the Lord who is about to speak to it in the Gospel and professes its faith by means of the chant. It is sung by all while standing and is led by the choir or a cantor, being repeated if this is appropriate. The verse, however, is sung either by the choir or by the cantor. The Alleluia is sung in every season other than Lent. The verses are taken from the Lectionary or the Gradual. During Lent, in place of the Alleluia, the verse before the Gospel is sung, as indicated in the Lectionary. It is also permissible to sing another psalm or tract, as found in the Gradual.
When there is only one reading before the Gospel, During a season when the Alleluia is to be said, either the Alleluia Psalm or the responsorial Psalm followed by the Alleluia with its verse may be used; During the season when the Alleluia is not to be said, either the psalm and the verse before the Gospel or the psalm alone may be used; The Alleluia or verse before the Gospel may be omitted if they are not sung.
The Sequence, which is optional except on Easter Sunday and on Pentecost Day, is sung before the Alleluia.