The poet and critic Randall Jarrell said of his poetry, "William Carlos Williams is as magically observant and mimetic as a good novelist. He reproduces the details of what he sees with surprising freshness, clarity, and economy; and he sees just as extraordinarily, sometimes, the forms of this earth, the spirit moving behind the letters. His quick transparent lines have the nervous and contracted strength, move as jerkily and intently as a bird." R. P. Blackmur said of Williams poetry "the Imagism of 1912 , self-transcended."
Williams's major collections are Spring and All (1923), The Desert Music and Other Poems (1954), Pictures from Brueghel and Other Poems (1962), and Paterson (1963, repr. 1992). His most anthologized poem is "The Red Wheelbarrow", an example of the Imagist movement's style and principles (see also "This Is Just To Say"). However, Williams, like his peer and friend Ezra Pound, had already rejected the Imagist movement by the time this poem was published as part of Spring and All in 1923.
Williams is strongly associated with the American modernist movement in literature and saw his poetic project as a distinctly American one; he sought to renew language through the fresh, raw idiom that grew out of America's cultural and social heterogeneity, at the same time freeing it from what he saw as the worn-out language of British and European culture. In 1920, this project took shape in Contact, a periodical launched by Williams and fellow writer Robert McAlmon: "The two editors sought American cultural renewal in the local condition in clear opposition to the internationalists—Pound, The Little Review, and the Baroness." Yvor Winters, the poet/critic, judged that Williams's verse bears a certain resemblance to the best lyric poets of the 13th century.
Williams sought to invent an entirely fresh and uniquely American form of poetry whose subject matter centered on everyday circumstances of life and the lives of common people. He came up with the concept of the "variable foot" which Williams never clearly defined, although the concept vaguely referred to Williams's method of determining line breaks. The Paris Review called it "a metrical device to resolve the conflict between form and freedom in verse."
One of Williams's aims, in experimenting with his "variable foot", was to show the American (opposed to European) rhythm that he claimed was present in everyday American language. Stylistically, Williams also worked with variations on a line-break pattern that he labeled "triadic-line poetry" in which he broke a long line into three free-verse segments. A well-known example of the "triadic line [break]" can be found in Williams's love-poem "Asphodel, That Greeny Flower."
In a review of Herbert Leibowitz's biography of William Carlos Williams, "Something Urgent I Have to Say to You": The Life and Works of William Carlos Williams, book critic Christopher Benfey wrote of Williams's poetry: "Early and late, Williams held the conviction that poetry was, in his friend Kenneth Burke's phrase, 'equipment for living, a necessary guide amid the bewilderments of life.' The American ground was wild and new, a place where a blooming foreigner needed all the help he could get. Poems were as essential to a full life as physical health or the love of men and women." Williams expressed this viewpoint most famously in a line from his poem "Asphodel, That Greeny Flower" in which he wrote:
It is difficult to get the news from poems yet men die miserably every day for lack of what is found there.