An apostolic nunciature is a top-level diplomatic mission of the Holy See that is equivalent to an embassy. However, it neither issues visas nor has consulates.

The head of the apostolic nunciature is called a nuncio, an ecclesiastical diplomatic title. A papal nuncio (officially known as an apostolic nuncio) is a permanent diplomatic representative (head of diplomatic mission) of the Holy See to a state or to one of two international intergovernmental organizations, the European Union or ASEAN, having the rank of an ambassador extraordinary and plenipotentiary, and the ecclesiastical rank of titular archbishop. Papal representatives to other intergovernmental organizations are known as "permanent observers" or "delegates".

In several countries that have diplomatic relations with the Holy See, the apostolic nuncio is ipso facto the dean of the diplomatic corps. The nuncio is first in the order of precedence among all the diplomats accredited to the country, and he speaks for the diplomatic corps in matters of diplomatic privilege and protocol. Most countries that concede priority to the nuncio are officially Catholic, but some are not.

In addition, the nuncio serves as the liaison between the Holy See and the Church in that particular nation. The nuncio has an important role in the selection of bishops.