Cia-Cia, also known as (South) Buton or Butonese, is an Austronesian language spoken principally around the city of Baubau on the southern tip of Buton island, off the southeast coast of Sulawesi, in Indonesia. It is written using the Latin and Hangul scripts.

In 2012, there were 105,000 speakers of Cia-Cia, many of whom also used Wolio, which is closely related to Cia-Cia, as well as Indonesian. Wolio is falling into disuse as a written language among the Cia-Cia, as it is written using the Arabic script, and Indonesian is now taught in schools using the Latin script.^{[unreliable source?]}

In two of the approximately 75 Cia-Cia-speaking subdistricts, the language has been privately taught to schoolchildren using the Hangul script since 2008. The students are also taught some basic Korean. The program remained active as of 2025.

Cia-Cia is spoken in Southeast Sulawesi, south Buton Island, Binongko Island, and Batu Atas Island.

According to legend, Cia-Cia speakers on Binongko descend from Butonese troops sent by a Butonese sultan.

The name of the language comes from the negator cia, "no". It is also known as Buton, Butonese, Butung, and in Dutch Boetonees, names it shares with Wolio, and as South(ern) Buton or Butung. The ambiguous name "Buton", often referring generically to various ethnic and linguistic groups of the Buton area, is said to be of Ternatese origin (butu – "market", "marketplace"). Names such as "South Buton" can be used to disambiguate from Wolio, the historically dominant language of the island.

The language situation on the island of Buton is very complicated and not known in great detail.

Dialects include Kaesabu, Sampolawa (Mambulu-Laporo), Wabula (with its subvarieties), and Masiri. The Masiri dialect shows the greatest amount of vocabulary in common with the standard dialect. The Pedalaman dialect uses gh—equivalent to r in other dialects—in native vocabulary, and r in loan words.^{[page needed]}