Imagism was a movement in early-20th-century poetry that favoured precision of imagery and clear, sharp language. It is considered the first organized modernist literary movement in the English language. Imagism has been termed "a succession of creative moments" rather than a continuous or sustained period of development. The French academic René Taupin remarked that "it is more accurate to consider Imagism not as a doctrine, nor even as a poetic school, but as the association of a few poets who were for a certain time in agreement on a small number of important principles".

The Imagists rejected the sentiment and discursiveness typical of Romantic and Victorian poetry. In contrast to the contemporary Georgian poets, who were generally content to work within that tradition, Imagists called for a return to more Classical values, such as directness of presentation, economy of language, and a willingness to experiment with non-traditional verse forms; Imagists used free verse. A characteristic feature of the form is its attempt to isolate a single image to reveal its essence. This mirrors contemporary developments in avant-garde art, especially Cubism. Although these poets isolate objects through the use of what the American poet Ezra Pound called "luminous details", Pound's ideogrammic method of juxtaposing concrete instances to express an abstraction is similar to Cubism's manner of synthesizing multiple perspectives into a single image.

Imagist publications appearing between 1914 and 1917 featured works by many of the most prominent modernist figures in poetry and other fields, including Pound, H.D. (Hilda Doolittle), Amy Lowell, Ford Madox Ford, William Carlos Williams, F. S. Flint, and T. E. Hulme. The Imagists were centred in London, with members from Great Britain, Ireland and the United States. Somewhat unusually for the time, a number of women writers were major Imagist figures.

The origins of Imagism are to be found in two poems, Autumn and A City Sunset by T. E. Hulme. These were published in January 1909 by the Poets' Club in London in a booklet called For Christmas MDCCCCVIII. Hulme was a student of mathematics and philosophy; he had been involved in setting up the club in 1908 and was its first secretary. Around the end of 1908, he presented his paper A Lecture on Modern Poetry at one of the club's meetings. Writing in A. R. Orage's magazine The New Age, the poet and critic F. S. Flint (a champion of free verse and modern French poetry) was highly critical of the club and its publications.

From the ensuing debate, Hulme and Flint became close friends. In 1909, Hulme left the Poets' Club and started meeting with Flint and other poets in a new group which Hulme referred to as the "Secession Club"; they met at the Eiffel Tower restaurant in London's Soho to discuss plans to reform contemporary poetry through free verse and the tanka and haiku and through the removal of all unnecessary verbiage from poems. The interest in Japanese verse forms can be contextualized by the late Victorian and Edwardian revival of Chinoiserie and Japonism as witnessed in the 1890s vogue for William Anderson's Japanese prints donated to the British Museum as well as in the influence of woodblock prints on paintings by Monet, Degas and van Gogh. Direct literary models were available from a number of sources, including F. V. Dickins's 1866 Hyak nin is'shiu, or, Stanzas by a Century of Poets, Being Japanese Lyrical Odes, the first English-language version of the Hyakunin Isshū, a 13th-century anthology of 100 waka, the early 20th-century critical writings and poems of Sadakichi Hartmann, and contemporary French-language translations.

The American poet Ezra Pound was introduced to the group in April 1909 and found their ideas close to his own. In particular, Pound's studies of early European vernacular poetry had led him to an admiration of the condensed, direct expression that he detected in the writings of Arnaut Daniel, Dante, and Guido Cavalcanti, amongst others. For example, in his 1911–12 series of essays I gather the limbs of Osiris, Pound writes of Daniel's line "pensar de lieis m'es repaus" ("it rests me to think of her"), from the canzone En breu brizara'l temps braus: "You cannot get statement simpler than that, or clearer, or less rhetorical". These criteria—directness, clarity and lack of rhetoric—were to be amongst the defining qualities of Imagist poetry. Through his friendship with Laurence Binyon, Pound had already developed an interest in Japanese art by examining Nishiki-e prints at the British Museum, and he quickly became absorbed in the study of Japanese verse forms.

In a 1915 article in La France, French critic Remy de Gourmont described the Imagists as descendants of the French Symbolists. Pound emphasised that influence in a 1928 letter to the French critic and translator René Taupin. He pointed out that Hulme was indebted to the Symbolist tradition, via W. B. Yeats, Arthur Symons and the Rhymers' Club generation of British poets and Mallarmé. Taupin concluded in his 1929 study that however great the divergence of technique and language "between the image of the Imagist and the 'symbol' of the Symbolists[,] there is a difference only of precision". In 1915, Pound edited the poetry of another 1890s poet, Lionel Johnson. In his introduction, he wrote

No one has written purer imagism than [Johnson] has, in the line
Clear lie the fields, and fade into blue air,
It has a beauty like the Chinese.