AMBASSADOR, a public minister of the first rank, ac credited and sent by the head of a sovereign State as his personal representative to negotiate with a foreign Government, and to watch over the interests of his own nation abroad. The power thus conferred is defined in the credentials or letters of credence of which the ambassador is the bearer, and in the instructions under the sign-manual delivered to him. The credentials consist of a sealed letter addressed by the sovereign whom the ambas sador represents to the sovereign to whom he is accredited, and they embody a general assurance that the sovereign by whom the ambassador is sent will confirm whatever is done by the ambas sador in his name. In Great Britain letters of credence are under the royal sign-manual, and are not countersigned by a minister.
It was agreed by the Congress of Vienna, 1815, that three classes of diplomatic agents should be recognized; and a fourth class was added by the Congress of Aix-la-Chapelle. There are, therefore, now four classes of diplomatic agents: (1) Ambassadors, including papal legates and nuncios, who enjoy the highest rank and are deemed to represent the person and dignity of the sovereign or head of their State, and who are entitled to personal access to the sovereign or head of the State to which they are accredited; (2) ministers plenipotentiary and envoys extraordinary, in cluding papal internuncios, who are accredited to the head of the State, and may also be resident, but who do not represent the person and dignity of the head of their own State; (3) ministers resident, who are accredited to the head of the State, but rank below the last class in their official position and dignity ; and (4) Charges d'affaires who are accredited by the Minister of Foreign Affairs to the Minister of Foreign Affairs and who may be appointed ad hoc or ad interim. It was also agreed that diplo matic agents of the same class should take precedence according to the date of the presentation of their credentials, but in Catho lic countries (except in France since the abrogation of the con cordat) precedence is usually given to the papal legate. The senior minister is the doyen or dean of the "diplomatic corps," and it is his function to see that the diplomatic privileges and immunities are duly observed.
Ambassadors were formerly accredited only to States enjoying royal honour. Later they were accredited also to republics re garded as of equal rank. By an act of Congress in 1893 the Presi dent of the United States was empowered to accredit ambassadors to the Great Powers. Great Britain sends diplomatic agents of the first class only to II States, Argentina being the last so promoted.
An ambassador, however, unless specially armed with plenary authority, cannot decide any questions beyond his instructions without reference to his government. Thus Lord Londonderry (Lord Stewart), who represented Great Britain at the confer ences of Troppau in 182o and Laibach in 1821, had not the same standing as the plenipotentiaries of the other Powers present, and efforts were even made to exclude him from some of the more important discussions in consequence, not on the ground of inferior rank, but of defective powers. For the special immunities and privileges of ambassadors see EXTERRITORIALITY and DIPLO MACY. See also the latter for the history of the subject.
BIBLIOGRAPHY.-Charles de Martens, Manuel diplomatique (Paris, Bibliography.-Charles de Martens, Manuel diplomatique (Paris, 1822 ; new ed. 1868). See also Henry Wheaton, Hist. of the Law of Nations (New York, 1845) ; Sir E. Satow, A Guide to Diplomatic Practice (1922).