Diplomacy is the art and practice of conducting negotiations between representatives of groups or states. It usually refers to international diplomacy, the conduct of international relations through the intercession of professional diplomats with regard to issues of peace-making, trade, war, economics and culture. International treaties are usually negotiated by diplomats prior to endorsement by national politicians.

The word stems from the Greek word "diploma", which literally means 'folded in two'. In ancient Greece, a diploma was a certificate certifying completion of a course of study, typically folded in two. In the days of the Roman Empire, the word "diploma" was used to describe official travel documents, such as passports and passes for imperial roads, that were stamped on double metal plates. Later, the meaning was extended to cover other official documents such as treaties with foreign tribes. In the 1700s the French called their body of officials attached to foreign legations the corps "diplomatique". The word "diplomacy" was first introduced into the English language by Edmund Burke in 1796, based on the French word "diplomatie".

In an informal or social sense, diplomacy is the employment of tact to gain strategic advantage or to find mutually acceptable solutions to a common challenge, one set of tools being the phrasing of statements in a non-confrontational, or polite manner.

Diplomats and diplomatic missions

A diplomat is someone involved in diplomacy; the collective term for a group of diplomats from a single country who are resident in another country is a diplomatic mission. Ambassador is the most senior diplomatic rank; a diplomatic mission headed by an ambassador is known as an embassy, with the exception of permanent missions at the United Nations, the Organization of American States, or other multilateral organizations, which are also headed by ambassadors. The collective body of all diplomats of particular country is called that country's diplomatic service. The collective body of all diplomats assigned to a particular country is the diplomatic corps. (See also diplomatic rank.)

Europe

The ability to practice diplomacy is one of the defining elements of a state, and diplomacy has been practiced since the first city-states were formed millennia ago. For most of human history diplomats were sent only for specific negotiations, and would return immediately after their mission concluded. Diplomats were usually relatives of the ruling family or of very high rank in order to give them legitimacy when they sought to negotiate with the other state.

One notable exception involved the relationship between the Pope and the Byzantine Emperor; papal agents, called apocrisiarii, were permanently resident in Constantinople. After the 8th century, however, conflicts between the Pope and Emperor (such as the Iconoclastic controversy) led to the breaking of close ties.