According to Redemptionis Sacramentum, an extraordinary minister of Holy Communion is a layperson formally instituted to administer - that is, distribute - Holy Communion during the Roman Catholic Mass. They are referred to as extraordinary as the ordinary ministers of Holy Communion are ordained clergy: Bishops, Priest and Deacons. According to instructions by the Vatican, they should only be used when truly necessary, i.e., where there are not enough ordinary ministers available, or any instituted acolytes.

The common use of Extraordinary Ministers of Holy Communion occurs, in some opinions, much more frequently than is permitted by the documents of the Church. It is common for at least one minister to assist a priest to distribute communion at all masses, which some argue means that they cease to be extraordinary. Their use in this case is only permitted where the priest (or, if other ordinary ministers are present) would cause a considerable delay if he were to distribute alone. There use is also proliferated by the regular distribution of Communion under the species of both bread and wine. Some consider that where there is only one ordinary minister, this practice should only take place occasionally to preserve the "extraordinary" nature of this ministry. The document "Redemptionis Sacramentum" would seem to support these views.

Acolytes are considered to be Extraordinary Ministers of Communion at all times and places, whereas ordinary lay persons are restricted in where and to whom they might administer the Sacrament. However, as most instituted acolytes are seminarians, the instance is rare. The subdeacon's role in the Eastern Catholic Churches is roughly equal to this practice, especially in the Middle East amongst Melkite and Maronite Catholics.

Extraordinary ministers were originally called "special ministers of the Eucharist" (Immensae Caritatis, 1973), and were frequently referred to as "Eucharistic ministers" or "extraordinary ministers of the Eucharist" until the 2004 instruction Redemptionis Sacramentum, n. 156 reprobated these usages.