The Vienna Convention on Diplomatic Relations stipulates that diplomatic relations between countries and the establishment of permanent embassies must be conducted by agreement. The level of diplomatic representatives is also determined by agreement between the two parties. For the diplomatic representatives that the sending country intends to send, the receiving country can accept a person it is willing to accept or reject an unpopular person (personanon grata) without giving a reason for the rejection. In order to avoid the adverse consequences of public rejection, a country always seeks advice in advance when sending diplomatic representatives. Solicitation of opinions through diplomatic channels, either orally or in writing, is an internationally recognized procedure for receiving envoys. Usually when soliciting opinions, a resume of the appointee is sent. The receiving country must respond within a short period of time. The candidates for diplomatic representatives who need to be consulted are mainly the head of the embassy, ??that is, the ambassador, minister or charge d'affaires who serves as the head of the mission, and the military attachés of the army, navy and air force. The consent of the receiving State is not required for the appointment of other staff in the embassy.

After the diplomatic representative obtains the consent of the receiving country, he can take office with his credentials and submit them to the receiving country. A letter of credence, or a sending letter of credence, is a formal document proving that the appointed person is a diplomatic representative dispatched by the head of state or the Ministry of Foreign Affairs of the sending country to the head of state or the Ministry of Foreign Affairs of the receiving country. Documents issued by an ambassador or minister are signed by the head of state and countersigned by the minister of foreign affairs. The agent's credentials are signed by the Minister of Foreign Affairs. Generally speaking, the diplomatic representative must personally deliver the letter of credence to the head of state or foreign minister of the receiving country, and eulogies and replies are also exchanged between the diplomatic representative and the head of state of the receiving country. The ceremony for submitting credentials used to be quite grand, but now it has been greatly simplified. According to international practice, a diplomatic representative must be considered to have started performing business after submitting his credentials. The ranking of diplomatic envoys at the same level, the so-called priority, is determined according to the time of submission of credentials. If the level of the diplomatic representative changes, or the head of state who originally issued the credentials dies, or the state structure of the sending country or the host country changes, the credentials need to be submitted again.

Diplomatic representatives who attend international conferences, hold negotiations, and sign treaties must have credentials. Credentials are documents signed by a head of state certifying the identity of a diplomatic representative and specifically granting him full authority to perform that task. According to international practice, except for heads of state, heads of government and foreign ministers, any other official who attends international meetings or holds negotiations is generally required to have credentials. In the past, international conferences only tested the credentials; now, most of them leave the completed credentials to the government or international organization of the country where the treaty is signed.