This thesis is a description, analysis and functional interpretation of voice and argument structure in Yaqui, a Uto-Aztecan language spoken in Southern Arizona and Sonora, Mexico. Yaqui is a SOV language with a complex verbal morphology, and voice alternations are morphologically marked. I begin with the analysis of argument structure in basic clause types, and describe lexical and clitic arguments. The voice alternates I identify are Passive, Impersonal, Anti-passive, Impersonal Anti-Passive and Unaccusative. I also provide an analysis of Dative and Applicative constructions, and a type of Possessive sentence where the head of the Possessed NP is incorporated into the verb. Each of these construction types has a specific function in discourse. The speaker selects the construction type that places an argument with a particular theta role in focus position, determines what other arguments are present, and determines which arguments are referential. This functional perspective gives us an integrated view of voice and argument type in Yaqui.