diplomatic courier

A diplomatic courier is a state agent entrusted with the physical conveyance of official correspondence, documents, and articles for official use (collectively, the diplomatic bag) between a government and its embassies, consulates, or delegations abroad. The institution is codified primarily in Article 27 of the Vienna Convention on Diplomatic Relations (1961) and, for consular channels, Article 35 of the Vienna Convention on Consular Relations (1963).

Key legal features include:

• Personal inviolability: the courier may not be arrested or detained while performing duties.
• Protection of the bag: the diplomatic bag itself shall not be opened or detained, and its packages must bear visible external marks of their character.
• Official document: the courier must carry an official document indicating status and the number of packages constituting the bag.
• Ad hoc couriers: a state may designate a courier for a single journey; immunities cease once the bag is delivered.
• Captain of a commercial aircraft: may be entrusted with the bag but is not considered a diplomatic courier.

In practice, couriers are used to transmit material too sensitive for electronic channels — encryption keys, classified cables, personnel files, signed originals of treaties, and sealed ballots for overseas voting. Major foreign services such as the U.S. Diplomatic Courier Service (within the Bureau of Diplomatic Security) and the UK's Queen's/King's Messengers maintain professional courier corps who travel almost continuously.

Disputes over the bag persist: receiving states occasionally suspect abuse — smuggling of weapons, currency, or persons — but the Convention provides no right of forcible inspection, only the option to request that the bag be opened in the presence of an authorized representative or returned. The 1989 ILC Draft Articles on the Status of the Diplomatic Courier and the Diplomatic Bag sought to consolidate the regime but were never adopted as a binding treaty.