CIO may refer to:
The Revolt of the Ciompi was a rebellion among unrepresented labourers which occurred in Florence, Italy from 1378 to 1382. Those who revolted consisted of artisans, labourers, and craftsmen who did not belong to any guilds and were therefore unable to participate in the Florentine government.
Ciomadul is a volcano in Romania, and is known as Csomád in Hungarian. It is in the Carpathians, close to the towns of Băile Tușnad and Bixad.
CIOO-FM is a Canadian radio station, broadcasting at 100.1 FM in Halifax, Nova Scotia. The station uses the on-air brand name C100. It was owned by Toronto based CHUM Limited until that company's buy-out by CTVglobemedia in 2007, and then Bell Media in 2011. CIOO's studios are located at the intersection of Russell and Agricola Streets in Halifax (right behind TV sister CJCH), with its transmitter located on Washmill Lake Drive in Clayton Park.
Ciona intestinalis (sometimes known by the common name of vase tunicate) is an ascidian (sea squirt), a tunicate with very soft tunic.
Cioppino is a fish stew originating in San Francisco, California. It is considered an Italian-American dish, and is related to various regional fish soups and stews of Italian cuisine.
Ciona is a genus of sea squirts in the family Cionidae.