||This dissertation provides a linguistic description and analysis of Desano, an endangered Tukanoan language of the Vaupes region of Brazil. Much valuable knowledge would be lost if this language were to become extinct without documentation. Several of the Tukanoan languages in the upper Amazon are highly endangered. The Eastern Tukanoan people are famous for their linguistic exogamy and ‘obligatory’ multilingualism; there are some twenty languages in the region whose speakers must marry someone who speaks a different language. There are a number of linguistic traits in Desano described in this dissertation which are of particular interest to linguists in general, because they are rare in the world’s languages, and they stand to contribute much to our understanding of the full range of possibilities in human grammar (and consequently also of some of the limits of human cognition). These include: nasal harmony (in phonology), the noun classifier system (in morphology), and the evidential system (in the interface of morphology-syntaxsemantics). The dissertation begins with an introduction of the Desano people and their language; including sociolinguistic information and some historical background. The second chapter presents a phonological description. It then proceeds with a description of the parts of speech in Desano and the characterization of the ‘word’ in Desano, in Chapter 3. The bulk of the dissertation is devoted to the morphosyntax of Desano, with chapters devoted to nominal morphology and verbal morphology.