Abstract. The kinship terminological systems documented for modern Ralá-muli (Tarahumara), a Southern Uto-Aztecan language, exhibit considerable dialectal and subdialectal diversity in both the terms they include and the linguistic forms of these terms-a diversity best understood in relation to the Proto-Tarahumaran kinship system. We reconstruct this antecedent system and discuss the principal changes that occurred in it between the seventeenth and late nineteenth centuries, when the Proto-Tarahumaran speech community appears to have still been intact. Many of the lexical, phonological, morphological, semantic, and structural differences that distinguish the modern systems from one another, like the emergence of the modern Ralámuli dialects, can be linked to the disruption of interaction patterns during the late nineteenth and twentieth centuries that resulted in the breakup of the Proto-Tarahumaran speech community.