The Establishment is a generalized, mostly negative term used in Western societies to refer to the controlling (elite) structures of those societies. The "establishment" is often said to be holding a lock on wealth and political power. Mostly est. is used as its abbreviation. The old boy's network has roughly the same connotations.

An "establishment" is often understood to compose an elite group of wealthy, influencial families, many of whom are involved in politics and business. They are often friends with one another, or at least very involved in and aware of each others' affairs. As a result, they are expected to be a generally cooperative group that works together to maintain a status quo that most favours their interests.

In the 1960s and 1970s, the "establishment" was seen as representing restrictive, authoritarian policies. It was associated with age, as the old fashioned way of doing things, and was said to be dominated by members of the war generation who had not yet adapted or accepted the big societial changes of the decade.

There may be different establishments within different institutions. For example, candidates for political office are often said to have to impress the "party establishment" in order to win endorsement.

An establishment can also mean a place of business or residence, the founding of such a place, or the founding of a business.

The first amendment to the United States Constitution forbids Congress from making any law with respect to an "establishment of religion." Here the term "establishment" refers to an entity similar to the Church of England, with which the Constitution's authors were quite familiar. This so-called "Establishment Clause" complements the first amendment's protection of the "free exercise" of religion, by limiting government entanglement with religion (whereas the "Free Exercise Clause" is more focused on preserving individual freedom of conscience).

Sociologically, one who does not belong to "the establishment", is an "outsider" - see Norbert Elias, The Established and the Outsiders (1965), and Scientific Establishments and Hierarchies (ed. with others) (1982).

See also: anti-establishment, The Establishment (club), Great and the Good, The Man