An ambassador, in diplomacy, is both a role and a rank. In the role of ambassador, Country A's ambassador is considered the diret representative of the head of state of Country A to Country B. The ambassador and other accredited diplomats have diplomatic immunity. The rules of diplomatic conduct are principally defined by the Vienna Convention on Diplomatic Relations
The ambassador will normally reside in the capital of Country B. The physical residence of the ambassador is the embassy, and is considered to be under the laws of country A. If the diplomatic mission to a country, as is often the case, has an office building(s) separate from the ambassador's residence, it is called the chancery, and also is subject to diplomatic immunity.
Role as Chief of Mission
Competition among officials of the ambassador's nation
Major powers often have multiple senior individuals in a foreign capital, and it variously may not be clear who has the real power, or the officials may fight over it. During the Vietnam War, President John F. Kennedy made a clear declaration that the Ambassador headed all agencies in the United States Mission to the Republic of Vietnam.
In Soviet embassies, the KGB Station Chief, or rezident, often had more actual power than the Ambassador. With the admittedly artificial state of an occupation, the Iraq War was complicated when head of the civilian Coalition Provisional Authority, L. Paul Bremer, and the senior military general, Ricardo Sanchez, had completely separate reporting chains. U.S. military and civilian forces in Afghanistan and Iraq also do not have a single head, but they seem to have close working relationships between the ambassador and senior military commander.
In countries with a professional diplomatic service, the highest rank is Ambassador, or a closely related term. Persons of ambassadorial rank may represent their country in international organizations such as the United Nations and its major agencies, in bilateral or multilateral negotiations on specific issues, advise a regional military commander, or other functions requiring the highest level of knowledge, experience, and skills at communications and negotiation.
- Vienna Convention on Diplomatic Relations and Additional Protocols, 18 April 1961
- Career Ambassador in the U.S. Foreign Service.