In diplomacy, an attaché is a person who is assigned ("to be attached") to the diplomatic or administrative staff of a higher placed person or another service or agency. Although a loanword from French, in English the word is not modified according to gender.

An attaché is normally an official, who serves either as a diplomat or as a member of the support staff, under the authority of an ambassador or other head of a diplomatic mission, mostly in intergovernmental organizations or international non-governmental organisations or agencies. Attachés monitor various issues related to their area of specialty (see examples below) that may require some action. To this end, attachés may undertake the planning for events to be attended, decisions which will be taken, managing arrangements and agendas, conducting research, and acting as a representative of the interests of their state when necessary, to the types of organizations mentioned above, and also to national academies and to industry.

Sometimes an attaché has special responsibilities or expertise. Examples include a cultural attaché, customs attaché, police officer attaché, labor attaché, legal attaché, liaison officer attaché, military/defense attaché, press attaché, agricultural attaché, commercial attaché, maritime attaché and science attaché.