This volume is the definitive reference grammar of an endangered Algonquian language spoken primarily in Wyoming and Oklahoma. Arapaho differs strikingly from other Algonquian languages, making it particularly relevant to the study of historical linguistics and the evolution of grammar. Cowell and Moss document Arapaho's interesting features, detail strategies used by speakers of this highly polysynthetic language to form complex words, and illustrate how word formation interacts with information structure. They discuss word order and discourse-level features, treat the special features of formal discourse style and traditional narratives, and list gender-specific particles, which are widely used in conversation. Appendices include full sets of inflections for a variety of verbs. With The Arapaho Language, Cowell and Moss have produced a comprehensive document of a language that, in its departures from its nearest linguistic neighbors, sheds light on the evolution of grammar.