An extraordinary minister of Holy Communion is an acolyte, or another of Christ's faithful deputed in certain circumstances, to distribute Holy Communion. The term "extraordinary" distinguishes such a person from the ordinary (normal, regular) minister of Holy Communion, namely a bishop, priest or deacon.

Canon law permits that "[w]here the needs of the Church require and ministers are not available, lay people, even though they are not lectors or acolytes, can supply certain of their functions, that is, exercise the ministry of the word, preside over liturgical prayers, confer baptism and distribute Holy Communion, in accordance with the provisions of the law." The term "lay people" does not distinguish between men and women. The extraordinary minister's function is to distribute Holy Communion, either within Mass or by taking it to a sick person.

An instituted acolyte (usually a seminarian) is an extraordinary minister of Holy Communion by virtue of his institution. The local bishop may delegate other lay Catholics for this function either for a single occasion or for a specified period of time, if there are reasons of real necessity. The commissioning need not take a liturgical form, but an appropriate blessing, which should in no way resemble ordination, may be imparted. In special cases of an unforeseen nature, the priest celebrating Mass may grant permission for a single occasion.