Paul VI, P. (1966). On liturgy in choir duty: Letter of Pope Paul VI to superiors general of clerical religious institutes bound by the obligation of choir duty. National Catholic Welfare Conference.

Paul VI, Pope. On Liturgy in Choir Duty: Letter of Pope Paul VI to Superiors General of Clerical Religious Institutes Bound by the Obligation of Choir Duty. Washington, D.C.: National Catholic Welfare Conference, 1966.

Paul VI, Pope. On Liturgy in Choir Duty: Letter of Pope Paul VI to Superiors General of Clerical Religious Institutes Bound by the Obligation of Choir Duty. National Catholic Welfare Conference, 1966.