The Diplomatic Service
There are two styles of address for individuals in the diplomatic and commonwealth service: formal and social. In almost all circumstances the social form of address is acceptable - that is a polite but slightly less deferential style of approach than the very rigid form that was followed in the last century. The formal styles of address may be found in the published edition of Debrett's Correct Form.
The collective term for a group of diplomats residing in another county is a diplomatic mission. Any diplomat who heads a diplomatic mission is known as chief of mission or head of mission. They are normally Ambassadors.
A diplomatic mission headed by an Ambassador is known as an embassy; a diplomatic mission headed by a High Commissioner is known as a high commission.
Internationally recognised diplomatic ranks were agreed at the Congress of Vienna in 1815. Ambassador is the most senior diplomatic rank, and Ambassadors are formal representatives of the Head of State. In commonwealth countries, the equivalent of the Ambassador is normally the High Commissioner.
Most Ambassadors represent their government in a single country; 'Ambassadors-at-large' work in several (normally neighbouring) countries, or represent their nation at intergovernmental organisations.
Underneath the Ambassador in the diplomatic hierarchy come the following: Minister; Minister-Counsellor; Counsellor; First Secretary; Second Secretary; Third Secretary; Attaché; Assistant Attaché.
The Chargé d'Affaires is normally the Ambassador's second-in command, and is responsible for the diplomatic mission in the absence of a more senior diplomat.
Attachés are generally staff, acting in an advisory or administrative capacity, who are not members of their country's diplomatic service, and are therefore temporarily 'attached' to the mission.
A Consul is appointed to represent the government of one state in the territory of another, and is responsible for looking after the welfare of the citizens of his/her own country in a foreign land. A consul differs from an Ambassador, who represents his/her head of state in a foreign country, and is concerned with diplomatic relations between the two nations.
Consuls are based in consulates (which may be within the Embassy itself).
How To Address...
Agent-General (representing Australian states within the UK)