Holy Orders in the Catholic Church includes three orders: bishop, priest, and deacon. The Church regards ordination as a Sacrament. In the phrase "Holy Orders", the word "holy" simply means "set apart for some purpose." The word order (ordo, in Latin) designates an established civil body or corporation with a hierarchy, and ordination means legal incorporation into an ordo. In context, therefore, a Holy Order is simply a group with a hierarchical structure that is set apart for ministry in the Church.

For Catholics, it is typically in the last year of seminary training that a man will be ordained to the "transitional diaconate." This distinguishes men bound for priesthood from those who have entered the "permanent diaconate" and do not intend to seek ordination as a priest. Deacons, whether transitional or permanent. receive faculties to preach, to perform baptisms, and to witness marriages. They may assist at the Eucharist or the Mass, but are not the ministers of the Eucharist.

After six months or more as a transitional deacon, a man will be ordained to the priesthood. Priests are able to preach, perform baptisms, witness marriages, hear confessions and give absolutions, anoint the sick, and celebrate the Eucharist or the Mass.

Some priests are later chosen to be bishops; bishops may ordain priests.