I have seen some priests at the altar wear the stole over the chasuble while others wear it underneath. Is this a matter of personal choice for the priest or are there rules about this practice?
The General Instruction of the Roman Missal, paragraph 299 describes "the chasuble, worn over the alb and stole" as the proper vestment for the priest at Mass. Paragraph 209 of the General Instruction of the Roman Missal notes: "In the vesting room or other suitable place, the concelebrants put on the sacred vestments they customarily wear when celebrating Mass individually. Should, however, a good reason arise, (e.g., a large number of concelebrants or a lack of vestments), concelebrants other than the principal celebrant may omit the chasuble and simply wear the stole over the alb." The Congregation for Divine Worship and the Discipline of the Sacraments is the Instruction, Redemptionis Sacramentum notes: "... Out of necessity the concelebrants other than the principal celebrant may even put on white chasubles. For the rest, the norms of the liturgical books are to be observed." (124) This same Instruction notes " the abuse is reprobated whereby the sacred ministers celebrate Holy Mass or other Rites without sacred vestments or with only a stole over the monastic cowl or the common habit of religious or ordinary clothes, contrary to the prescriptions of the liturgical books, even when there is only one minister participating.