Walter Alison Phillips

“ Officers and officials of the highest rank have the title of “high excellency.” Finally, in Italy, the title eccelenza, which had come to be used in the republics of Venice and Genoa as the usual form of address to nobles, has become as meaningless as the English title of “esquire” or the address of “sir,” being, especially in the south, the usual form of address to any stranger.
In the diplomatic service the title of excellency is technically reserved to ambassadors, but in addressing envoys also this form is commonly used by courtesy. ”

“ In the United States it is part of the official style of the governors of states, but not of that of the president; though diplomatic usage varies in this respect, some states (e.g. France) conceding to him the style of “excellency,” others (e.g. Belgium) refusing it. ”

“ The custom of other republics differs: in France the president is addressed as excellence by courtesy; in Switzerland the title is omitted; in the South American republics it is part of the official style (Pradier-Fodéré, Cours de droit diplom. i. 89) . In Spain the title of excelencia properly belonged to the grandees and to those who had the right to be covered in the royal presence, but it was extended also to high officials, viceroys, ministers, captains-general, lieutenants-general, ambassadors and knights of the Golden Fleece. ”