Letter of credence
A letter of credence is a formal letter, usually sent by one head of state to another, that formally grants diplomatic accreditation to a named individual to be the sending country's ambassador in the receiving country. A letter of recall is the opposite, recalling an ambassador, either as a means of diplomatic protest (see letter of protest) or because the diplomat is being replaced by another envoy. Diplomatic letters are generally written in French (the lingua franca of diplomacy), unless the countries share the same official language.
Letters of credence are presented personally to the receiving head of state by ambassador-designates in a formal ceremony. Letters serve as the most traditional and universal forms of Diplomatic credentials. Until their credentials are accepted, an ambassador-designate does not formally assume diplomatic status, including the possession of diplomatic immunity. In practice, however, they are almost invariably accepted, as both states will have informally discussed the issue in advance and sorted out any problems.