Horace's Ars Poetica (also known as "The Art of Poetry", Epistula Ad Pisones, or Letters to Piso), published c. 18 BC, was a treatise on poetics. It was first translated into English by Ben Jonson. Three quotes in particular are associated with the work:

The latter two phrases occur back-to-back, near the end of the treatise.

The work is also key for its discussion of the principle of decorum (using appropriate vocabulary and diction in each style of writing), and for Horace's criticisms of purple prose.

The best known poem by Archibald MacLeish (1892-1982), published in 1926, took its title and subject from Horace's work. His poem "Ars Poetica" contains the line "A poem should not mean/but be", which was a classic statement of the modernist aesthetic. The original manuscript of the poem resides in the Library of Congress.

Nobel Prize Polish writer Miłosz also wrote a poem with this title (1961), though his poem has a question mark at the end of the title.

The term "ars poetica" can refer to devices of metalanguage. The definition of "ars poetica" in the past decade extends to defining techniques of rhetoric, including but not limited to: writing about writing, singing about singing, thinking about thinking, etc. Stemming first from poetry on poetry, "ars poetica" is now widely used as a literary device to enhance imagery, understanding, or profundity.

Moreover, the technique of "ars poetica" was previously an attempt to capture the essence of poetry through poetry; the poet would write his poem, then step back, and his poem would become a way of knowing, of seeing, albeit through the senses, the emotions, and the imagination. In the modern century, a passage of writing or composition employing an "ars poetica" style is one that tries to capture the essence, the intrinsic value, of what it is expressing through. A song about a song, for example, would be an attempt to manifest the fleeting beauty of lyrics, notes, and dynamics.