A diplomatic mission or foreign mission is a group of people from a state or organization present in another state to represent the sending state or organization officially in the receiving or host state. In practice, the phrase usually denotes an embassy or high commission, which is the main office of a country's diplomatic representatives to another country; it is usually, but not necessarily, based in the receiving state's capital city.

Consulates, on the other hand, are smaller diplomatic missions that are normally located in major cities of the receiving state (but can be located in the capital, typically when the sending country has no embassy in the receiving state). In addition to being a diplomatic mission to the country in which it is located, an embassy may also be a non-resident permanent mission to one or more other countries.

The term embassy is sometimes used interchangeably with chancery, the physical office or site of a diplomatic mission. Consequently, the terms "embassy residence" and "embassy office" are used to distinguish between the ambassador's residence and the chancery.

A country may have several different types of diplomatic missions in another country.

The head of an embassy 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 operates 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 nomenclature for their missions and staff: a Vatican mission is headed by a nuncio (Latin for "envoy") and consequently known as an apostolic nunciature. Under the rule of Muammar Gaddafi, Libya's missions used the name people's bureau, headed by a secretary.

Missions between Commonwealth countries are known as high commissions, and their heads are high commissioners. Generally speaking, ambassadors and high commissioners are regarded as equivalent in status and function, and embassies and high commissions are both deemed to be diplomatic missions.