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.

[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.

[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.