The official form of address of an ambassador is usually the form used to address a head of state: “Your Excellency”, followed by the name or country represented. In many countries, less formal variants are often used, such as “ambassador” followed by the name or the name followed by “ambassador of… ». In the United States, “Mister/Madam Ambassador” can be used. An ambassador is an official envoy, especially a high-ranking diplomat, who represents a state and is usually accredited to another sovereign state or international organization as a resident representative of its own government or sovereign, or appointed for a special and often temporary diplomatic task.  The word is also used informally to refer to people known to represent certain professions, activities and fields of activity, such as sales, without national nominations. Since members of the Commonwealth of Nations have or have had a common head of state, they do not exchange ambassadors, but have high commissioners who represent the government, not the head of state. The diplomat representing the Holy See bears the title of nuncio. In diplomatic parlance, the High Commissioner and the Nuncio are equated with an ambassador of rank and role. Resident coordinators of the United Nations system are accredited to the Head of State and have the same rank as ambassadors. The equivalent of an ambassador exchanged between members of the Commonwealth of Nations is known as high commissioners. Ambassadors of the Holy See are known as apostolic or apostolic nuncios.
An ambassador is the most senior diplomatic officer appointed by the government as its resident representative in a foreign state or before an international organization. The main tasks of ambassadors are to maintain diplomatic relations with the receiving state and to promote foreign policy strategies through international organizations. Among other things, ambassadors ensure the safety of their citizens living in the host country, strive to establish and maintain strong diplomatic and economic relations with foreign countries, and administer all embassy affairs. States usually have ambassadors in most countries with which they have diplomatic relations, and the embassy is usually located in the capital of the host country. An ambassador is the most senior government official stationed in a capital city or foreign country. The host country usually allows the ambassador to control a specific area called an embassy, whose territory, personnel, and vehicles usually enjoy diplomatic immunity in the host country. According to the Vienna Convention on Diplomatic Relations, an ambassador has the highest diplomatic rank. Countries may choose to maintain lower-level diplomatic relations by appointing a chargé d`affaires instead of an ambassador. In some countries, a former ambassador may be designated and called ambassador throughout his or her life (in the United States, one may hear “Mr. Ambassador” or “Madam Ambassador”).
In other countries, ambassador is a title that is due to its holder only in relation to a specific position and cannot be used after leaving or outside the position. Some countries do not use the term when an ambassador is in the country of origin because the incumbent is not an ambassador. For example, a Canadian ambassador who is in Canada is generally not referred to as an ambassador, although he or she is referred to as “Canada`s ambassador to.. can be described; i.e. in relation to a specific professional function; Such a person may be designated as ambassador only during the performance of his or her duties. Due to the advent of modern technologies, today`s world is relatively smaller. With this in mind, it is considered important that the nations of the world have at least a small staff living in foreign capitals to assist travelers and visitors from their home countries. As an agent of the diplomatic service, an ambassador is supposed to protect the citizens of his home country in the host country.   The foreign government to which an ambassador is assigned must first approve the individual. In some cases, the foreign government could revoke its consent by declaring the diplomat persona non grata, that is, an unacceptable person. This type of declaration usually results in the recall of the ambassador to his country of origin. According to the Vienna Congress of 1815 and the Vienna Convention on Diplomatic Relations of 1961, the ambassador and embassy staff enjoy diplomatic immunity and personal security when living abroad.
  An ambassador is a diplomatic official sent abroad by a country, state or sovereign ruler, with a legal commission and the authority to conduct business on behalf of his or her country. In the past, presidents or prime ministers have appointed special diplomatic envoys for specific tasks, mainly abroad, but sometimes also inside the country as ambassadors. Another result of increased outbound travel is the growth of trade between nations. For most countries, the economy is now part of the global economy. This means increased opportunities to sell and trade with other countries. When two countries engage in trade, it is generally advantageous for both parties to have an ambassador and perhaps a small staff in the other country where they act as intermediaries between cooperative enterprises.   The 1961 Vienna Convention on Diplomatic Relations formalized the system and is the international law used today. According to this, ambassadors are highest-ranking diplomats who officially represent their head of state, with authorized powers (i.e. full authority to represent the government). In modern parlance, most ambassadors abroad as heads of mission bear the full title of ambassador extraordinary and plenipotentiary.