DIPLOMATIC AGENT. – An organ of the political relations between States, entrusted with representing, either temporarily or permanently, the sending State in the State where the agent exercises his functions. The use of occasional and transitory embassies dates back to the most remote antiquity. It was only in the second half of the 17th century, however, that the practice became general among States of exchanging permanent diplomatic representatives (the first permanent representation was that established by the Republic of Venice in Genoa in 1455). This practice has assumed such a general and regular character that the right of active and passive legation is spoken of as an attribute of international personality, and it is debated whether this “right” also belongs to entities other than States and the Holy See. It must be excluded, however, that the exchange of diplomatic agents between two States constitutes an object of right and obligation.
Diplomatic agents are distinguished into ordinary and extraordinary. This distinction sets over against one another, on the one hand, those invited with a permanent character, who have the task of safeguarding the interests of the sending State in the State where they are located, observing and reporting to their government, acting as intermediaries in communications, overseeing the observance of commitments assumed toward their government by the foreign government, conducting negotiations, protecting nationals residing there, etc.; and on the other hand, those sent without a permanent character, entrusted with special missions, such as the stipulation of a treaty, the presentation of public apologies, an official proposal of marriage, etc.; or the representation of the State at a congress, a conference (delegates), or an official ceremony.
According to the regulations adopted at the Congress of Vienna (protocol of the session of 9 March 1815 and additional protocol of Aix-la-Chapelle of 21 Nov. 1818), intended to put an end to questions of precedence that often gave rise to controversy, diplomatic agents are classified into four categories in order of importance: 1) ambassadors, to whom are equated legates and papal nuncios; 2) extraordinary envoys, ministers plenipotentiary, and internuncios; 3) resident ministers (class added at the Congress of Aix-la-Chapelle); 4) chargés d’affaires: the envoys of the first three classes accredited to the Head of State, and chargés d’affaires accredited to the minister of foreign affairs. According to the Vienna Regulations (art. 2), only the first category has representative character; but this distinction, which derives from the quality of personal representatives of the Sovereign originally attributed to ambassadors, is understood in the sense that only ambassadors represent, in addition to the State, also the person of the accrediting Head of State, and this is translated only into ceremonial prerogatives. The agents of the above-listed categories are only the heads of diplomatic missions whose members have increased in number and variety of functions in step with the development of international relations. Normally a mission is composed, in addition to the head, of counsellors, secretaries and attachés, chancellors, and other official personnel.
The diplomatic agents accredited to a State form the diplomatic corps, at the head of which, by tradition and express provision of the Vienna protocol, is the papal nuncio or the highest-ranking or most senior of the lay agents. The sole substantial function of the diplomatic corps is to oversee the observance, by the local government, of the immunities and privileges pertaining to its members. The diplomatic mission, a term that designates the period during which the diplomatic agent exercises his functions in a State or at the Holy See, officially begins after the two States have manifested their respective desire to send and receive the agent with the presentation of the letters of credence (v.), preceded, for the first three classes of agents, by the agrément (v.) or “assent” of the receiving State; it ends with the completion of the mission (extraordinary invitation); with the recall by the sending State; with the rupture of diplomatic relations; with the outbreak of war between the two States; or for personal or administrative reasons that determine the substitution of the envoy.