The Seneca language is a member of the Iroquoian language family. Seneca is a seriously endangered language spoken in upper New York State and Southern Ontario. This book consists of 3 parts. Section I, on orthography, describes a way of writing Seneca words consistently and without omitting features that are significant. Various spelling systems have been used, and are being used, for the writing of Seneca by missionaries, anthropologists, and the speakers of the language themselves. Section II, on grammar, is concerned with the structure of Seneca words. Section III is a brief glossary of the Seneca language.