"Do not go gentle into that good night" is a poem in the form of a villanelle by Welsh poet Dylan Thomas (1914–1953), and is one of his best-known works. Though first published in the journal Botteghe Oscure in 1951, the poem was written in 1947 while Thomas visited Florence with his family. The poem was subsequently included, alongside other works by Thomas, in In Country Sleep, and Other Poems and Collected Poems, 1934–1952. The poem entered the public domain on 1 January 2024.

A villanelle, also known as villanesque, is a nineteen-line poetic form consisting of five tercets followed by a quatrain. There are two refrains and two repeating rhymes, with the first and third lines of the first tercet repeated alternately at the end of each subsequent stanza until the last stanza, which includes both repeated lines. The villanelle is an example of a fixed verse form. The word derives from Latin, then Italian, and is related to the initial subject of the form being the pastoral.