A concept with two deep roots — Hegelian and Marxist — that have since fused into a general critical vocabulary for describing the experience of being estranged from what ought to be one's own: one's labor, one's products, one's fellow humans, one's self.
For G. W. F. Hegel, alienation (Entfremdung) is a necessary moment in Spirit's historical self-realization: consciousness confronts as alien an objectivity that is in fact its own product, and the overcoming of this estrangement is the dialectical motor of progress. The young Karl Marx of the 1844 Economic and Philosophic Manuscripts took over this scheme and grounded it in the concrete conditions of wage labor. Under capitalism, he argued, the worker is alienated in four interlocking ways: from the product of his labor (owned by the capitalist, sold back to him as a commodity); from the activity of labor (performed under direction, for another's purposes, as a means to bare survival); from his species-being (the human capacity for free, conscious, creative production); and from other humans (relations among workers and between workers and capitalists are mediated by commodity exchange rather than cooperation).
The 1844 Manuscripts were not published until 1932, and their rediscovery reshaped 20th-century Marxism. Western Marxists (Lukács, Herbert Marcuse, the The Frankfurt School) made alienation central again, often extending it beyond wage labor into consumer culture, bureaucracy, and mass society. Existentialists (Simone de Beauvoir) developed related accounts of how specific social arrangements (gender, race, colonial relations) produce the experience of being estranged from one's own possibilities. Contemporary republican and recognition theorists (Honneth) have extended the vocabulary further.
The concept's persistent appeal is that it names something phenomenologically real — the feeling of being forced through the day by forces that are nominally one's own doing — in a way that rights-talk and utility-talk do not quite capture.