Geoffrey Kimball presents the first grammar of the American Indian language Yukhiti Koy, better known in English as Atakapa, once spoken in coastal southwestern Louisiana and coastal eastern Texas. The late eighteenth and early nineteenth centuries saw a drastic fall in the Atakapa population, and by the first decades of the twentieth century the Atakapa language ceased to be spoken. The grammar is based on the field notes collected by Albert Samuel Gatschet in January of 1885, with additional material collected by John R. Swanton in 1907-8. Gatschet worked with two speakers of the language, Kisyuc, also known as Yoyot, and her cousin Tottoks, whose English names were Louison Huntington and Delilah Moss, respectively. John R. Swanton wrote a grammatical sketch of Atakapa in 1929 based on Gatschet's notes and in 1932 published the texts Gatschet had gathered, as well as a dictionary. The materials, originally written phonetically, have been phonemicized, and the nature of the grammar has been elucidated. The nine surviving texts in Yukhiti have been phonemicized, analyzed, and translated, and the parallels between them and other traditional oral literatures of Native American languages of the Southeast are discussed. This reference grammar includes a vocabulary of all words contained in the field notes.