Mutsun (also known as San Juan Bautista Costanoan) is a Utian language spoken in Northern California. It was the primary language of a division of the Ohlone people living in the Mission San Juan Bautista area. The Tamien Nation and Amah Mutsun [Wikidata] band is currently working to restore the use of the language, using a modern alphabet.^[2][3][4]

Maria Ascención Solórsano de Garcia y de Cervantes, the last known fluent speaker of Mutsun, amassed large amounts of language and cultural data specific to the Mutsun.^[3] The Spanish Franciscan missionary and linguist Felipe Arroyo de la Cuesta wrote extensively about the language's grammar, and linguist John Peabody Harrington made very extensive notes on the language from Solórsano. Harrington's field notes formed the basis of the grammar of Mutsun written by Marc Okrand as a University of California dissertation in 1977^[1] which to this day remains the only grammar^{[citation needed]} ever written of any Costanoan language. Scholars from the U.S., Germany, and the Netherlands have discussed methods that could facilitate the revitalization of Mutsun.^[5]

Vowel and consonant phonemes are represented here with the descriptions and orthography of the English-Mutsun dictionary,^[6] with additions from an earlier paper by Warner, Butler, and Luna-Costillas.^[7]