Book excerpt: This book investigates the contact between Arawak and Tucanoan languages spoken in the Vaupés river basin in northwest Amazonia, which spans Colombia and Brazil. In this region language is seen as a badge of identity: language mixing is resisted for ideological reasons. The book considers which parts of the language categories are likely to be borrowed. This study also examines changes brought about by recent contact with European languages and culture, and the linguistic effects of language obsolescence.