Warihío is a spoken Uto-Aztecan language with two dialects. Upland Warihío is found in the mountains of Chihuahua. River Warihío is spoken along the Mayo River in Sonora, Mexico. Together with Yaqui, Mayo and the various Tarahumara dialects, Warihío makes up the Taracahitic sub-group of the Sonoran branch of Uto-Aztecan. All field and supporting data here come from the River dialect. This grammatical outline touches on all major aspects of River Warihío, including a brief description of its phonology, major and minor word classes, simple sentence structure, voice, and complex sentences structure. The description and analysis of voice phenomena, including passives, causatives, and applicatives, follows Shibatani´s theoretical framework. Also included is a brief section comparing some relevant aspects of Warihío grammar with Uto-Aztecan languages. The author received his Bachelor and Master degrees in Linguistics from the Universidad de Sonora, México. His Master’s Thesis was on Yaqui Grammatical Relations. He received a Ph.D. in Linguistics from Rice University. The author has published several articles on Warihío, and Yaqui grammatical and information structures.