Diplomatic correspondence

Diplomatic correspondence is correspondence between one state and another, usually – though not exclusively – of a formal character. It follows several widely observed customs and style in composition, substance, presentation, and delivery and can generally be categorized into letters and notes.

Letters are correspondence between heads of state, typically used for the appointment and recall of ambassadors; for the announcement of the death of a sovereign or an accession to the throne; or for expressions of congratulations or condolence.

Letters between two monarchs will typically begin with the salutation "Sir My Brother" (or "Madame My Sister", in the case of a female monarch) and close with the valediction "Your Good Brother" (or sister, in the case of a female monarch), unless one monarch is of inferior rank to the other (if, for instance, the Grand Duke of Luxembourg were to correspond to the Queen of the United Kingdom) in which case the inferior monarch will use the salutation "sire" while the superior monarch may refer to the other as "cousin" instead of "brother". A letter from a monarch to the head-of-state of a republic, vice versa, or of the head-of-state from one republic to another, may begin with the salutation "My Great and Good Friend" and close with the valediction "Your Good Friend"; beneath the signature line will be inscribed "To Our Great and Good Friend [Name and Title of Recipient]".

A letter of credence (lettres de créance) or credentials is the instrument by which a head of state exercises his or her power to appoint ("accredit") ambassadors and ministers to foreign countries. The letter of credence is signed by the sending head of state and is addressed to the receiving head of state. (In some countries, letters accrediting or recalling ambassadors or ministers are also countersigned by a minister of state).

The particular elements of a letter of credence vary from country to country, but "the essence of any letter of credence is contained in the final phrase asking that credit may be given to all that the ambassador may say in the name of his sovereign or Government." Usually "the appointment and reception of diplomatic representatives are matters of protocol and ceremony" but there are occasionally "legal implications in the context of questions as to the legitimacy of a particular head of State" because addressing letters of credence to, or accepting letters of credence from, a foreign head of state has implications relating to recognition of a particular government. Letters of credence date to the thirteenth century.

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