A diplomatic mission is a group of people from one state or an international inter-governmental organisation (such as the United Nations) present in another state to represent the sending state/organisation in the receiving state. In practice, a diplomatic mission usually denotes the permanent mission, namely the office of a country's diplomatic representatives in the capital city of another country. As well as being a diplomatic mission to the country in which it is situated, it may also be a non-resident permanent mission to one or more other countries. There are thus resident and non-resident embassies.

A permanent diplomatic mission is typically known as an embassy, and the person in charge of the mission is known as an ambassador. The term "embassy" is often used to refer to the building or compound housing an ambassador's offices and staff. Technically, however, "embassy" refers to the diplomatic delegation itself, while the office building in which they work is known as a chancery.