Valid But Unlawful is a term unique to Roman Catholicism to describe the unauthorised ordinations of clergy. Under Roman Catholic theology a bishop ex-officio has an ability to ordain a man to be a deacon, priest or bishop. However to be lawful, that ability must be exercised in accordance with the wishes of the Church and the rules of Canon law. A Valid But Unlawful ordination, as the name suggests, is one where a bishop uses his valid ability to ordain someone whom under canon law or instruction from the pope he was prohibited from ordaining, it hence being unlawful.

A bishop who validly but unlawfully ordains someone, and the person who is ordained by him, are both automatically excommunicated.

In the twentieth century, French Catholic Archbishop Marcel Lefebvre earned automatic excommunication for his valid but unlawful ordinations of conservative catholic priests and bishops.

Less serious transgressions are sometimes designated, in Roman Catholic as well as Anglican churches, as 'valid but irregular'.