A permanent diplomatic mission is typically known as an Embassy, and the head of the mission is known as an Ambassador, or High Commissioner. The term "embassy" is commonly used also as a section of a building in which the work of the diplomatic mission is carried out, but, strictly speaking, it is the diplomatic delegation itself that is the embassy, while the office space and the diplomatic work done is called the Chancery. Therefore, the Embassy is in the Chancery.
The members of a diplomatic mission can reside within or outside the building that holds the mission's chancery, and their private residences enjoy the same rights as the premises of the mission as regards inviolability and protection.
All missions to the United Nations are known simply as permanent missions, while EU Member States' missions to the European Union are known as permanent representations and the head of such a mission is typically both a permanent representative and an ambassador. European Union missions abroad are known as EU delegations. Some countries have more particular naming for their missions and staff: a Vatican mission is headed by a nuncio (Latin "envoy") and consequently known as an apostolic nunciature. Under the rule of Muammar Gaddafi, Libya's missions used the name "people's bureau" and the head of the mission was a secretary.
Today, an embassy is the nerve center for a country's diplomatic affairs within the borders of another nation, serving as the headquarters of the chief of mission, staff and other agencies. An embassy is usually located in the capital city of a foreign nation; there may also be consulates located in provincial or regional cities.
U.S. embassies and consulates abroad, as well as foreign embassies and consulates in the United States, have a special status. While diplomatic spaces remain the territory of the host state, an embassy or consulate represents a sovereign state. International rules do not allow representatives of the host country to enter an embassy without permission --even to put out a fire -- and designate an attack on an embassy as an attack on the country it represents.
Missions between Commonwealth countries are known as high commissions and their heads are High Commissioners. This is because Ambassadors are exchanged between foreign countries, but since the beginning of the Commonwealth, member countries have nominally maintained that they are not foreign to one another (the same reason as the naming of the Foreign and Commonwealth Office). An ambassador represents one head of state to another and an ambassador's letters of credence are addressed by one head of state to another. Until India became a republic on 26 January 1950, all members of the Commonwealth had the same head of state, making the appointment of ambassadors between them impossible. The senior representative of a Commonwealth country to another was therefore called a high commissioner, accredited not to the head of state but to the government of the receiving country, but at the same time considered the equivalent of an ambassador. Still today, even if two Commonwealth countries have distinct heads of state (Presidents), each one's senior diplomatic representative to the other continues to be called a high commissioner, whether he or she represents a sending government or a sending head of state.
In the past a diplomatic mission headed by a lower-ranking official (an envoy or minister resident) was known as a legation. Since the ranks of envoy and minister resident are effectively obsolete, the designation of legation is no longer used today.