This is a comprehensive description of the Kwaza language of Southern Rondonia, in the Brazilian Amazon. Kwaza is not clearly related to any other known language. Until recently, almost nothing was known about Kwaza and with only 25 remaining speakers this indigenous language is likely to become extinct some time this century. Moreover, the history and the culture of its speakers are otherwise undocumented. The present work is part of an attempt to preserve the Kwaza language. Part I deals with the grammar of Kwaza in detail and gives an overview of its social, cultural and historical context. Part II contains a selection of Kwaza texts with morphological analyses and free translations. Part III is a dictionary of Kwaza, with many examples and an English-Kwaza register.