A Papal Nuncio (also known as an Apostolic Nuncio) is a permanent diplomatic representative (head of mission) of the Holy See to a state, having ambassadorial rank.
Internuncios (also heads of missions) rank below nuncios, being of the rank of an envoy or minister, while a legate a latere is a temporary papal representative or a representative for a special purpose. Historically, an apocrisiary was a nuncio to the Byzantine Empire; during the fifth and sixth centuries, during which much of Italy remained under Byzantine control, many Popes were former apocrisiaries.
A Pro-Nuncio is a diplomatic representative who is not of full ambassadorial rank, his status representing the nature of the diplomatic relationship between the Holy See and the state to which he has been assigned. Until recent times a Pro-Nuncio served as the papal representative to the United States and the United Kingdom. Both states in the late twentieth century upgraded their relationship with the Holy See to full ambassadorial level, allowing for the appointment of a papal nuncio.
The Vienna Convention on Diplomatic Relations provides that (article 14(2)) "Except as concerns precedence and etiquette, there shall be no differentiation between heads of mission by reason of their class." Some states give special precedence to representatives of the Holy See, which they are permitted to do by the Convention (article 16(3)) "This article is without prejudice to any practice accepted by the receiving State regarding the precedence of the representative of the Holy See."
In 1902 the papal Internuncio of Brazil was raised to the dignity of nuncio.
This privilege of papal envoys was expressly recognized by the Congress of Vienna in 1815 and is universally observed.
From the first half of the sixteenth century, when the bureau of the papal secretary of state was fully developed and the permanent nunciatures received their ultimate organization, the reports of the nuncios were sent regularly (from the middle of the sixteenth century, often weekly).
A PapalNuncio (also known as an Apostolic Nuncio) is a permanent diplomatic representative (head of mission) of the Holy See to a state or international organisation (e.g., the Arab League), having ambassadorial rank, usually with the ecclesiastical rank of titular bishop or titular archbishop.
A legate a latere is a temporary papal representative or a representative for a special purpose.
Historically, the most important type of apocrisiary (a title also applying to representatives exchanged by a high prelate with a Patriarch) was the equivalent of a nuncio, sent by the Pope to the Byzantine Empire; during the fifth and sixth centuries, when which much of Italy remained under Byzantine control, several Popes were former apocrisiaries.