Institutio generalis Missalis Romani

Concelebration, which appropriately expresses the unity of the priesthood, of the Sacrifice, and also of the whole People of God, is prescribed by the rite itself for the Ordination of a Bishop and of priests, at the blessing of an abbot, and at the Chrism Mass. Unless the good of the Christian faithful requires or suggests otherwise, concelebration is also recommended at ^{101Cf. Second Vatican Ecumenical Council, Constitution on the Sacred Liturgy, Sacrosanctum Concilium, no. 57; Codex Iuris Canonici, can. 902.}