The priesthood is the office of the ministers of religion, who have been commissioned ("ordained") with the Holy orders of the Catholic Church. Technically, bishops are a priestly order as well; however, in layman's terms priest refers only to presbyters and pastors. The church's doctrine also sometimes refers to all baptised (lay) members as the "common priesthood", which can be confused with the ministerial priesthood of the consecrated clergy.

Ordination is the process by which individuals are consecrated, that is, set apart and elevated from the laity class to the clergy, who are thus then authorized to perform various religious rites and ceremonies. The process and ceremonies of ordination vary by religion and denomination. One who is in preparation for, or who is undergoing the process of ordination is sometimes called an ordinand. The liturgy used at an ordination is commonly found in a book known as an Ordinal which provides the ordo for celebrations.