Free verse is an open form of poetry. It does not use consistent meter patterns, rhyme, or any other musical pattern. Many poems composed in free verse thus tend to follow the rhythm of natural speech. 
Poets have explained that free verse is not totally free; 'its only freedom is from the tyrant demands of the metered line'. Free verse displays some elements of form. Most free verse self-evidently continues to observe a convention of the poetic line in some sense, at least in written representations, though retaining a potential degree of linkage. Donald Hall goes as far as to say that "the form of free verse is as binding and as liberating as the form of a rondeau ", and T. S. Eliot wrote, "No verse is free for the man who wants to do a good job".
Kenneth Allott the poet/critic said the adoption by some poets of vers libre arose from 'mere desire for novelty, the imitation of Whitman, the study of Jacobean dramatic blank verse, and the awareness of what French poets had already done to the alexandrine in France'. The American critic John Livingston Lowes in 1916 observed 'Free verse may be written as very beautiful prose ; prose may be written as very beautiful free verse. Which is which?'
Some poets have considered free verse restrictive in its own way. In 1922 Robert Bridges voiced his reservations in the essay ' Humdrum and Harum-Scarum.' Robert Frost later remarked that writing free verse was like "playing tennis without a net." William Carlos Williams said "being an art form, verse cannot be free in the sense of having no limitations or guiding principles". Yvor Winters, the poet/critic said "the free verse that is really verse, the best that is, of W.C. Williams, H. D., Marianne Moore, Wallace Stevens, and Ezra Pound is the antithesis of free"
As the name vers libre suggests, this technique of using more irregular cadences is often said to be derived from the practices of 19th-century French poets such as Gustave Kahn and Jules Laforgue in his Derniers vers of 1890. Taupin, the USA based French poet/critic concluded that free verse and vers libre are not synonymous, since 'The French language tends to give equal weight to each spoken syllable, whereas English syllables vary in quantity according to whether stressed or unstressed'.
The sort of cadencing that we now recognize in free verse can be traced back at least as far as the Hebrew psalmist poetry of the Bible.  By referring to Psalms it is possible to argue that free verse in English first appeared in the 1380s in the John Wycliffe translation of the Psalms and was repeated in different form in most biblical translations ever since. Walt Whitman, who based his long lines in "Leaves of Grass" on the phrasing of the King James Bible, influenced later American free verse practitioners, notably Allen Ginsberg. One form of free verse was employed by Christopher Smart in a long poem called Jubilate Agno, written some time between 1759 and 1763 but not published until 1939.
Many poets of the Victorian era experimented with free verse. Christina Rossetti, Coventry Patmore, and T. E. Brown all wrote examples of rhymed but unmetered verse. Poems such as W. E. Henley's 'Discharged' (from his In Hospital sequence). Free verse in English was persuasively advocated by critic T. E. Hulme in his A Lecture on Modern Poetry (1908). Later in the preface to Some Imagist Poets 1916, he comments, "Only the name is new, you will find something much like vers libre in Dryden's Threnodia Augustalis ; a great deal of Milton's Samson Agonistes , and the oldest in Chaucer's House of Fame ." 
In France, a few pieces in Arthur Rimbaud's prose poem collection Illuminations were arranged in manuscript in lines, rather than prose and in the Netherlands, tachtiger (i.e. member of 1880s generation of innovative poets) Frederik van Eeden employed the form at least once (in his poem "Waterlelie" ["water lily"]  ).
Goethe (particularly in some early poems, such as " Prometheus ") and Hölderlin used free verse occasionally, due in part to a misinterpretation of the meter used in Pindar's poetry; in Hölderlin's case, he also continued to write unmetered poems after discovering this error.  The German poet Heinrich Heine made an important contribution to the development of free verse with 22 poems, written in two-poem cycles called 'Die Nordsee' (The North Sea) (written 1825-1826).  These were first published in Buch der Lieder (Book of Songs) in 1827.
Form and structure
Although free verse requires no meter, rhyme, or other traditional poetic techniques, a poet can still use them to create some sense of structure. A clear example of this can be found in Walt Whitman's poems, where he repeats certain phrases and uses commas to create both a rhythm and structure.
Pattern and discipline is to be found in free verse: the internal pattern of sounds, the choice of exact words, and the effect of associations give free verse its beauty.  With the Imagists free verse became a discipline and acquired status as a legitimate poetic form.  Herbert Read however, noting that 'the Imagist Ezra Pound gave free verse its musical structure to an extent that parodoxically it was no longer free'. 
Due to a lack of predetermined form, free verse poems have the potential to take truly unique shapes. Unrestrained by traditional boundaries, Yvor Winters described this as "attempts to widen experience by establishing 'abnormal' conventions", the poet possesses more license to express, and has more control over the development of the poem. This can allow for a more spontaneous and individualized poetic art product.
Technically, free verse has been described as 'spaced prose', a mosaic of verse and prose experience.