To defrock a priest is to deprive him of the right to exercise the functions of the priestly office. Various religions with priests have different procedures for doing this.

Roman Catholicism

The Council of Trent (session XIII, canon iv) declared that the sacrament of ordination, imbues the recipient with an indelible "priestly character". Therefore the return of an ordained priest to the lay state is absolutely impossible. However, laicization, which takes from a priest the licit (authorized) use of his powers, and other rights, can occur by various means.

A priest is automatically laicized when he marries or joins the military without permission. A priest may be voluntarily laicized by his superiors at his request. A priest may be involuntarily laicized for wrongdoing. Minor clerics, including priests, are laicized through the "penalty of degradation". Major clerics can be laicized by the Holy See.

Laicized priests are forbidden to wear clerical habit, identify themselves as priests, or administer the sacraments. The only exception would be to hear a confession in an emergency situation. They are required to continue practicing celibacy, although dispensations can be made. By laicization a priest loses the right of benefice, which in modern times means he will not be supported by the Church even after retirement.

A laicized priest still has the power to confect the Eucharist but cannot use it licitly.

Eastern Orthodoxy

In Eastern Orthodoxy, the laicization of a priest or monk, tied to the infringement of a sacred vow or unrepentant heresy, goes hand in hand with an anathema. This not only defrocks the former cleric but also banishes him from entering a holy shrine (Orthodox one most commonly), receive the Eucharist or be blessed by a priest.