Free verse (or vers libre) is a style of poetry that is based on cadences that are more irregular than those of traditional poetic meter. While traditional poetic forms are based on fixed stress-patterns and syllable counts, free verse is not constrained to use a fixed number of syllables for each line, and distributes its stress accents in irregular patterns. Free verse may or may not use rhyme. When it is used, it tends to follow a looser pattern than would be expected in formal verse.

The ideal of poets who write in free verse was well described by Ezra Pound, who wrote: "As regarding rhythm: to compose in the sequence of the musical phrase, not in sequence of a metronome." Pound's friend T. S. Eliot somewhat cryptically wrote: "No verse is free for the man who wants to do a good job."

Many formalist poets find free verse to be aesthetically useless, or, at the least, less capable of expression. One such poet, Robert Frost, said that writing free verse was like "playing tennis without a net".

As the name vers libre suggests, this technique of using more irregular cadences is often said to derive from the practices of 19th century French poets like Gustave Kahn. However, in English it can be traced back at least as far as the King James Bible. Walt Whitman, who based his verse approach on the Bible, was the major precursor for modern poets writing free verse, though they were reluctant to acknowledge his influence.