Rubāʿī (Persian: رباعی rubāʿī, "quatrain") is a poetry style. It is used to describe a Persian quatrain, or its derivative form in English and other languages. The plural form of the word, rubāʿiyāt (رباعیات), often anglicised rubaiyat, is used to describe a collection of such quatrains.
There are a number of possible rhyme schemes to the rubaiyat form, e.g. AABA, AAAA. In Persian verse, the ruba'i is usually written as a four-line (or two-couplet) poem, with rhymes at the middle and end of each line.
This is an example from Khayyam's Ruba'iyyat:
- Anwâr-é Salâhu'd-dîn bar angêkhta bâd
- dar dîda-wo jân-é `âshiq-ân rêkhta bâd
- har jân ke laTîf gasht-o az lutf gozasht
- bâ khâk-é Salâhu'd-dîn dar âmêkhta bâd
- (May the splendors of Salahuddin be roused,
- and poured into the eyes and souls of the lovers.
- May every soul that has become refined and has surpassed refinement
- Be mingled with the dust of Salahuddin!)
Ruba'i in English 
The verse form AABA as used in English verse is known as the Rubaiyat Quatrain due to its use by Edward FitzGerald in his famous 1859 translation, The Rubaiyat of Omar Khayyam. Algernon Charles Swinburne, one of the first admirers of FitzGerald's translation of Khayyam's medieval Persian verses, was the first to imitate the stanza form, which subsequently became popular and was used widely, as in the case of Robert Frost's 1922 poem "Stopping by Woods on a Snowy Evening".
Fitzgerald's translation became so popular by the turn of the century that hundreds of American humorists wrote parodies using the form and, to varying degrees, the content of his stanzas, including The Rubaiyat of Ohow Dryyam, The Rubaiyat of A Persian Kitten, The Rubaiyat of Omar Cayenne and The Rubaiyat of Omar Khayyam, Jr.
In extended sequences of ruba'i stanzas, the convention is sometimes extended so that the unrhymed line of the current stanza becomes the rhyme for the following stanza. The structure can be made cyclical by linking the unrhymed line of the final stanza back to the first stanza: ZZAZ. These more stringent systems were not, however, used by FitzGerald in his Rubaiyat.
- The word is derived from Arabic رباعي, from the root ر ب ع (r-b-ʿ), related to "four". JM Cowan, (editor). The Hans Wehr Dictionary of Modern Written Arabic, Spoken Language Services, 1976, ISBN 0-87950-001-8, p. 323
- A Brief History of Persian Literature, by the Iran Chamber Society
- Princeton Encyclopedia of Poetry and Poetics, Princeton University Press, 1974, p.611
- Introduction to The Rubaiyat of Omar Khayyam, translated by Peter Avery and John-Heath Stubbs, Penguin Classics, 1981, ISBN 0-14-044384-3, p. 9
- The Cambridge History of Iran, v. 4, edited by R. N. Frye, Cambridge University Press, 1999, ISBN 0-521-20093-8, pgs. 633-634
- Elwell-Sutton, L. P. "The Foundations of Persian Prosody and Metrics," Iran, v. 13 (1975), p. 92.
- "The Splendors of Salahuddin".
- Skelton, Robin (2002). The Shapes of Our Singing: A Comprehensive Guide to Verse Forms and Metres from Around the World. Spokane, WA: Eastern Washington University Press. p. 106. ISBN 0-910055-76-9.
- Turco, Lewis (2000). The Book of Forms: A Handbook of Poetics. Lebanon, NH: University Press of New England. p. 245. ISBN 1-58465-022-2.