The fifteen Katuic languages form a branch of the Austroasiatic languages spoken by about 1.3 million people in Southeast Asia. People who speak Katuic languages are called the Katuic peoples. Paul Sidwell is the leading specialist on the Katuic languages ^{[citation needed]}. He notes that Austroasiatic/Mon–Khmer languages are lexically more similar to Katuic and Bahnaric the closer they are geographically. He says this geographic similarity is independent of which branch of the family each language belongs to. He also says Katuic and Bahnaric do not have any shared innovations, so they do not form a single branch of the Austroasiatic family, but form separate branches.

In 1966, a lexicostatistical analysis of various Austroasiatic languages in Mainland Southeast Asia was performed by Summer Institute of Linguistics linguists David Thomas and Richard Phillips. This study resulted in the recognition of two distinct new subbranches of Austroasiatic, namely Katuic and Bahnaric (Sidwell 2009). Sidwell (2005) casts doubt on Diffloth's Vieto-Katuic hypothesis, saying that the evidence is ambiguous, and that it is not clear where Katuic belongs in the family. Sufficient data for use in the sub-classification of the Katuic languages only become available after the opening of Laos to foreign researchers in the 1990s.

Reconstructions of Proto-Katuic, or its sub-branches, include:

• Thomas (1967): A Phonology Reconstruction of Proto-East-Katuic
• Diffloth (1982): Registres, devoisement, timbres vocaliques: leur histoire en katouique
• Efinov (1983): Problemy fonologicheskoj rekonstrukcii proto-katuicheskogo jazyka
• Peiros (1996): Katuic Comparative Dictionary
• Therapahan L-Thongkum (2001): Languages of the Tribes in Xekong Province, Southern Laos
• Paul Sidwell (2005): The Katuic languages: classification, reconstruction and comparative lexicon

Sidwell (2005) reconstructs the consonant inventory of proto-Katuic as follows:

This is identical to reconstructions of proto-Austroasiatic except for *ʄ, which is better preserved in the Katuic languages than in other branches of Austro-Asiatic, and which Sidwell believes was also present in Proto-Mon Khmer.

Paul Sidwell (2015:185-186)^[4] lists the following lexical innovations unique to Katuic that had replaced original Proto-Austroasiatic forms.

Sidwell (2015:173) lists the following lexical isoglosses shared between Katuic and Bahnaric.

Furthermore, Gerard Diffloth (1992)^[7] lists the words 'centipede', 'bone', 'to cough', 'to fart', 'to breathe', and 'blood' as isoglosses shared between Katuic and Vietic. A Vieto-Katuic connection has also been proposed by Alves (2005).^[8]

• List of Proto-Katuic reconstructions (Wiktionary)

• Gehrmann, Ryan. 2018. Katuic presyllables and derivational morphology in diachronic perspective. In Ring, Hiram & Felix Rau (eds.), Papers from the Seventh International Conference on Austroasiatic Linguistics, 132–156. Journal of the Southeast Asian Linguistics Society Special Publication No. 3. Honolulu: University of Hawai’i Press.
• Gehrmann, Ryan. 2017. The Historical Phonology of Kriang, A Katuic Language. Journal of the Southeast Asian Linguistics Society 10.1, 114–139.
• Gehrmann, Ryan. 2016. The West Katuic languages: comparative phonology and diagnostic tools. Chiang Mai: Payap University MA Thesis.
• Gehrmann, Ryan. 2015. Vowel Height and Register Assignment in Katuic. Journal of the Southeast Asian Linguistics Society 8. 56–70.
• Gehrmann, Ryan and Johanna Conver. 2015. Katuic Phonological Features. Mon-Khmer Studies 44. 55–67.
• Choo, Marcus. 2012. The Status of Katuic Archived 2019-06-26 at the Wayback Machine. Chiang Mai: Linguistics Institute, Payap University.
• Choo, Marcus. 2010. Katuic Bibliography with Selected Annotations Archived 2019-07-06 at the Wayback Machine. Chiang Mai: Linguistics Institute, Payap University.
• Choo, Marcus. 2009. Katuic Bibliography Archived 2019-11-09 at the Wayback Machine. Chiang Mai: Linguistics Institute, Payap University.
• Sidwell, Paul. 2005. The Katuic languages: classification, reconstruction and comparative lexicon Archived 2020-12-04 at the Wayback Machine. LINCOM studies in Asian linguistics 58. Munich: LINCOM Europa. ISBN 3-89586-802-7
• Sidwell, Paul. 2005. Proto-Katuic phonology and the sub-grouping of Mon-Khmer languages Archived 2019-11-11 at the Wayback Machine. In Paul Sidwell (ed.), SEALSXV: Papers from the 15th Meeting of the South East Asian Linguistics Society, 193–204. Pacific Linguistics PL E1. Canberra: Pacific Linguistics.
• Theraphan L-Thongkum. 2002. The Role of endangered Mon-Khmer languages of Xekong Province, Southern Laos, in the reconstruction of Proto-Katuic. In Marlys Macken (ed.), Papers from the Tenth Annual Meeting of the Southeast Asian Linguistics Society. 407–429. Program for Southeast Asian Studies, Arizona State University.
• Theraphan L-Thongkum. 2001. ภาษาของนานาชนเผ่าในแขวงเซกองลาวใต้. Phasa khong nanachon phaw nai khweng Sekong Lao Tai. [Languages of the tribes in Xekong province, Southern Laos]. Bangkok: The Thailand Research Fund.
• Peiros, Ilia. 1996. Katuic comparative dictionary. Pacific Linguistics C-132. Canberra: Australian National University. ISBN 0-85883-435-9
• Miller, John & Carolyn Miller. 1996. Lexical comparison of Katuic Mon-Khmer languages with special focus on So-Bru groups in Northeast Thailand. Mon-Khmer Studies 26. 255–290.
• Migliazza, Brian. 1992. Lexicostatistic analysis of some Katuic languages. In Amara Prasithrathsint & Sudaporn Luksaneeyanawin (eds.), 3rd International Symposium on Language and Linguistics, 1320–1325. Bangkok: Chulalongkorn University.
• Gainey, Jerry. 1985. A comparative study of Kui, Bruu and So phonology from a genetic point of view. Bangkok: Chulalongkorn University MA thesis.
• Effimov, Aleksandr. 1983. Проблемы фонологической реконструкции прото-катуического языка. Probljemy phonologichjeskoj rjekonstruktsii Proto-Katuichjeskovo jazyka. [Issues in the phonological reconstruction of the Proto-Katuic language]. Moscow: Institute of Far Eastern studies Moscow dissertation.
• Diffloth, Gérard. 1982. Registres, dévoisement, timbres vocaliques: leur histoire en Katouique. [Registers, devoicing, vowel phonation: their history in Katuic]. Mon-Khmer Studies 11. 47–82.
• Thomas, Dorothy. M. (1967). A phonological reconstruction of Proto–East Katuic. Grand Forks: University of North Dakota MA thesis.