Leaves of Grass is a poetry collection by American poet Walt Whitman (1819–1892), each poem of which is loosely connected and represents the celebration of his philosophy of life and humanity. Though first published in 1855, Whitman spent most of his professional life writing and rewriting Leaves of Grass,revising it multiple times until his death. This resulted in vastly different editions over four decades—the first edition being a small book of twelve poems, and the last, a compilation of over 400.

Influenced by Ralph Waldo Emerson and the Transcendentalist movement, itself an offshoot of Romanticism, Whitman's poetry praises nature and the individual human's role in it. Rather than relying on symbolism, allegory, and meditation on the religious and spiritual, like much of the poetry (especially English poetry) to come before it, Leaves of Grass (particularly the first edition) exalts the body and the material world instead. Much like Emerson, however, Whitman does not diminish the role of the mind or the spirit; rather, he elevates the human form and the human mind, deeming both worthy of poetic praise.

With one exception, its poems do not rhyme or follow standard rules for meter and line length. Among the works in this collection are "Song of Myself", "I Sing the Body Electric", and "Out of the Cradle Endlessly Rocking". Later editions would include Whitman's elegy to the assassinated President Abraham Lincoln, "When Lilacs Last in the Dooryard Bloom'd".