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 officially in the receiving state. A diplomatic mission usually denotes the resident 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.

The functions of a diplomatic mission consist, inter alia, in representing the sending State in the receiving State; protecting in the receiving State the interests of the sending State and of its nationals, within the limits permitted by international law; negotiating with the Government of the receiving State; ascertaining by all lawful means conditions and developments in the receiving State, and reporting thereon to the Government of the sending State; promoting friendly relations between the sending State and the receiving State, and developing their economic, cultural and scientific relations. - Vienna Convention on Diplomatic Relations