The term normally denotes an official, under the authority of an Ambassador or other head of a diplomatic mission, who serves either as a diplomat or as a member of the support staff. He monitors various issues related to areas of intervention. To this end, he undertakes the planning for decisions which will be taken and makes all necessary arrangements, manages the agenda, conducts research for the study of particular matters, and acts as representative when necessary.
Sometimes an attaché has special responsibilities or expertise, often specified by that field. Examples include a cultural attaché, labor attaché, legal attaché, military/defense attaché (or more specifically, naval attaché, air attaché), press attaché, agricultural attaché, and science attaché. Typically, a military attaché serves on the diplomatic staff of an embassy or consulate; however, during the Russo-Japanese War (1904-1905), for example, military and naval attachés served as "embedded" officers within the land and naval forces of both Russia and Japan.
The original connotation was that an attaché was an officer (employee) of another service 'attached to,' for example, an Embassy or Consulate. Thus, an attaché who holds a military commission would retain that commission despite being assigned to serve in an Embassy.
The title is used in other hierarchical administrations as well, for example, in the Roman Curia of the Catholic Church, in cases where a priest, usually in the diplomatic corps of the Holy See or else released for service to the Holy See, serves in a nunciature in a given country.
In the ministries of the Belgian federal state the term is used, since 2005 replacing the term adjunct-adviseur (in Dutch) or conseiller-adjoint (in French), normally used for college graduates, one rank under the head of a competence section.