Among the many ways in which sounds alternate in the world's languages, changes in the order of sounds (metathesis) are relatively rare. Mutsun, a Southern Costanoan language of California which was documented extensively before the death of its last speaker in 1930, displays three patterns of synchronic consonant-vowel (CV) metathesis. Two of these patterns appear to have remained productive while the language was actively spoken. In stem-deriving metathesis, many disyllabic noun stems ending in a VC string (as well as a few trisyllabic noun stems) alternate with semantically related verb stems ending in a CV string: e.g.,cayic ‘strength’ ~ cayci ‘to be strong’. In reflexive metathesis, a subset of verb stems, which are normally vowel-final in all environments, surface in consonant-final form in the presence of the reflexive suffix –pu and/or the reciprocal suffix -mu, as in kitro ‘to dress, to clothe’ ~ kitorpu ‘to get dressed, to dress oneself’. Finally, in suffix metathesis, the plural and locative suffixes (as well as the desiderative/irrealis enclitic) alternate between CCV and CVC forms depending on whether the preceding stem ends in a consonant or a vowel. Based on data from a large corpus of archival records of the language compiled over a span of more than a century, all three patterns of metathesis in Mutsun appear to defy the types of phonological analysis that have been proposed in the literature to account for metathesis in a variety of other languages. The phonetic and phonological factors claimed to motivate metathesis in other languages, such as misinterpretation of acoustic cues, stress attraction, sonority hierarchies, and positional restrictions, are absent in Mutsun. In this dissertation, I argue that prosodic analyses based on syllable weight and prosodic templates are required to account for Mutsun metathesis. Mutsun stem metathesis in particular has less in common, morphophonologically speaking, with metathesis in other languages than it does with reduplication or templatic morphology.