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.