The Composite order is a mixed order, combining the volutes of the Ionic order capital with the acanthus leaves of the Corinthian order. In many versions the composite order volutes are larger, however, and there is generally some ornament placed centrally between the volutes. The column of the composite order is typically ten diameters high, though as with all the orders these details may be adjusted by the architect for particular buildings. The Composite order is essentially treated as Corinthian except for the capital, with no consistent differences to that above or below the capital.

The Composite order is not found in ancient Greek architecture and until the Renaissance was not ranked as a separate order. Instead it was considered as an imperial Roman form of the Corinthian order. Though the Arch of Titus, in the forum in Rome and built in 82 AD, is sometimes cited as the first prominent surviving example of a composite order, the order was probably invented "a little before Augustus's reign, and certainly well-developed before his death, the very time when the Roman version of Corinthian was being established."

With the Tuscan order, a simplified version of the Doric order, also found in ancient Roman architecture but not included by Vitruvius in his three orders, the Composite was added by Renaissance writers to make five classical orders. Sebastiano Serlio (1475–1554) published his book I Sette libri dell'architettura in 1537 in which he was the second to mention the Composite order as its own order and not just as an evolution of the Corinthian order as previously suggested by Leon Battista Alberti. Leon Battista Alberti in his De re aedificatoria (English: On the Art of Building) mentions the Composite order, calling it "Italic".