The Luiseño language is a Uto-Aztecan language of California spoken by the Luiseño, a Native American people who at the time of first contact with the Spanish in the 16th century inhabited the coastal area of southern California, ranging 50 miles (80 km) from the southern part of Los Angeles County, California, to the northern part of San Diego County, California, and inland 30 miles (48 km). The people are called "Luiseño", owing to their proximity to the Mission San Luis Rey de Francia.

The language went extinct in the early 2010's, but an active language revitalization project is underway, assisted by linguists from the University of California, Riverside. The Pechanga Band of Luiseño Indians offers classes for children, and in 2013, "the tribe ... began funding a graduate-level Cal State San Bernardino Luiseño class, one of the few for-credit university indigenous-language courses in the country." In 2012, a Luiseño video game for the Nintendo DS was being used to teach the language to young people.

Linguist John Peabody Harrington made a series of recordings of speakers of Luiseño in the 1930s. Those recordings, made on aluminum disks, were deposited in the United States National Archives. They have since been digitized and made available over the internet by the Smithsonian Institution.

Luiseño has ten vowel phonemes, five long and five short.

Diphthongs include ey [ej], ow [ow] and oow [oːw].

Luiseño vowels have three lengths.

Overlong vowels are rare in Luiseño, typically reserved for absolutes, such as interjections, e.g. aaashisha, roughly "haha!" (more accurately an exclamation of praise, joy or laughter).

For some native speakers recorded in The Sparkman Grammar of Luiseño, the allophones [ə] and [ɨ] are free variants of [e] and [i] respectively. However, other speakers do not use these variants. Sparkman records fewer than 25 Luiseño words with either [ə] or [ɨ]. For one of these words (ixíla "a cough") the pronunciations [əxɨla] and [ɨxɨla] are both recorded.