A gatekeeper is a person who controls access to something, for example via a city gate or bouncer, or more abstractly, controls who is granted access to a category or status. Gatekeepers assess who is "in or out", in the classic words of management scholar Kurt Lewin.

Various figures in the religions and mythologies of the world serve as gatekeepers of paradisal or infernal realms, granting or denying access to these realms, depending on the credentials of those seeking entry. Figures acting in this capacity may also undertake the status of watchman, interrogator or judge. In the late 20th century the term came into metaphorical use, referring to individuals or bodies that decide whether a given message will be distributed by a mass medium.