The Sphinx is a 174-line poem by Oscar Wilde, written from the point of view of a young man who questions the Sphinx in lurid detail on the history of her sexual adventures, before finally renouncing her attractions and turning to his crucifix. It was written over a period of twenty years, stretching from Wilde's years as an Oxford student up to the poem's publication in an édition de luxe in 1894. The Sphinx drew on a wide range of sources, both ancient and modern, but particularly on various works of the French Decadent movement. Though at first coldly received by critics it is now generally recognized as Wilde's finest Decadent poem, and has been described as "unrivalled: a quintessential piece of fin-de-siècle art".

The poem begins with the narrator describing the figure of a sphinx which stands "in a dim corner of my room". He then addresses her, "Come forth you exquisite grotesque! half woman and half animal!", and asks to stroke her. He contrasts her immense antiquity with his own "twenty summers", and begins to enumerate scenes of Classical history and Egyptian mythology, asking her if she witnessed them. He next turns to the question "Who were your lovers? who were they who wrestled for you in the dust?" He suggests various Egyptian animals, mythical beasts, men, women and gods, before announcing "Nay, I know / Great Ammon was your bedfellow!" He details the beginning of their sexual liaison, and describes Ammon's personal beauty and splendour, before reflecting that that splendour has all come to ruin. He bids the sphinx return to Egypt to find and honour Ammon's remains; yet Ammon is not dead, and neither are any of her other divine lovers. In Egypt she could resume any of her former passions with god or beast. The narrator dismisses her with disgust both for her and for himself: "You make my creed a barren sham, you wake foul dreams of sensual life". Finally, he asks to be left to his crucifix with its figure of Christ, who "weeps for every soul who dies, and weeps for every soul in vain".

The writing of The Sphinx was a long and complicated process, lasting almost twenty years and producing eleven surviving groups of manuscripts. Wilde began working on it in 1874, the year he went up to Oxford, possibly in the summer of that year when he was on holiday in Paris with his parents. In 1883, again in Paris, he returned to the poem and produced a version which included thirteen stanzas not found in the published poem. By the 1890s Wilde, needing money and wanting to present himself as something more than a fiction-writer and journalist, brought his poem into its final form, ready for publication.

The Sphinx was published on 11 June 1894 by Elkin Mathews and John Lane in an edition of just 200 copies along with a large-paper edition limited to 25 copies. It was printed in black, green, and red, and boasted illustrations by Charles Ricketts, who also designed the vellum and gold binding. It has been described as "the most exquisite of all Wilde's first editions...so beautiful that, read in any other format, it seems to lose half of its power". Wilde dedicated the book to his friend Marcel Schwob, and remarked that "My first idea was to print only three copies: one for myself, one for the British Museum, and one for Heaven. I had some doubts about the British Museum."

The Sphinx was originally written in the four-line stanza, rhyming ABBA, used by Tennyson in his In Memoriam and by Wilde himself in very many of his poems. Later, by eliminating half of the line-breaks, he reduced the four eight-syllable lines of each stanza to two sixteen-syllable lines, thereby turning end rhymes into internal rhymes. In this form, as finally published, it is 174 lines in length.

The prime influence on The Sphinx was the French Decadent movement, particularly Huysmans' À rebours, the cat sonnets in Baudelaire's Les Fleurs du mal, and the poems of Maurice Rollinat. In particular, the poem's fascination with monsters, statues, and ambiguous sexuality draws on Flaubert's Tentation de Saint Antoine and on Gautier's Mademoiselle de Maupin and Émaux et camées; Flaubert also provided Wilde with much of his exotic vocabulary. Other important influences include Swinburne's "Dolores", with its "imputation of ageless profligacy"; Rossetti's "The Burden of Nineveh", itself inspired by the British Museum's acquisition of a sculptured god from Nineveh; and Shelley's "Ozymandias", recalling Wilde's "giant granite hand still clenched in impotent despair". The ending of Wilde's poem, in which the sphinx is seen as an evil presence and dismissed, echoes the ending of Poe's "The Raven", which may also have suggested some of The Sphinx's complex prosodic features. Wilde's "snake-tressed Fury" may be taken from Dante's Inferno. He did not make use of Egyptological scholarship, preferring, as a classicist, to take his view of Egypt from writers like Herodotus and Tacitus. Several books of the Bible provided Wilde with details, including Exodus, 2 Kings, Job, and Matthew.

The influence on The Sphinx of various art objects has also been traced. One example is Gustave Moreau's painting Oedipus and the Sphinx, in which, as described by Giles Whiteley, "the Sphinx is grasping onto the half naked body of Oedipus and gazing coquettishly into his eyes, repeating physically the coupling of Hermaphroditus and Salmacis". Wilde's lines

Sing to me of the Jewish maid who wandered with the Holy Child,
And how you led them through the wild, and how they slept beneath your shade.