A philosophical and literary current that emerged in 19th-century Europe and crystallized as a self-conscious movement in mid-20th-century France. Its unity is thematic rather than doctrinal — existentialists disagreed about almost everything except the questions that mattered — but its recurring preoccupations are unmistakable: the concrete, finite, choosing individual rather than abstract humanity; freedom as burden as much as blessing; the experience of anxiety, dread, absurdity, and death as disclosing something true rather than as pathologies to be managed away; and a suspicion of systems, especially the Hegelian kind, that would subsume the individual into some larger rational totality.
Its major ancestors are Søren Kierkegaard (writing in Copenhagen in the 1840s against Hegel, and making the leap of faith the paradigm act of existence) and Friedrich Nietzsche (diagnosing the death of God and demanding creative self-overcoming). In the 20th century, it took two distinct forms. The first was religious, running through Russian thinkers (Dostoevsky, Berdyaev, Shestov), through Paul Tillich's Protestant theology, and through Gabriel Marcel's Catholic personalism. The second was atheist, centered in postwar Paris, worked out by Jean-Paul Sartre, Simone de Beauvoir, Albert Camus, and Merleau-Ponty — though Camus always rejected the label and Heidegger (whose Being and Time was the decisive 20th-century text) rejected it more emphatically still.
By the 1960s the word itself had been so thoroughly commodified — existentialism as berets and cigarettes and vague anguish — that serious philosophers fled it. But its concerns outlived the label: they run through Walker Percy's novels, through Rollo May's psychology, through liberation theology, and through any philosophy that refuses to treat human life as a problem to be solved rather than a condition to be lived.