Yoloxóchitl Mixtec (YM) is charactized by its high number of tonal contrasts (nine basic tones and over twenty three lexical tonal melodies on bimoraic stems and, not unexpectedly, the almost complete absence of tonal sandhi. As in other Mixtec languages, tone in YM carries a high functional load: tonal contrasts not only mark the aforementioned aspect and mood distinctions but person marking as well. Despite the rich and unexplored occurrence of tonal alternations in derivational morphology, in this paper we limit our study of tone to the marking of mood and aspect on verbs, a marking that manifests a fairly high degree of morphological regularity. That is, specific tones are consistently associated to specific aspect/mood values. This chapter begins with a brief overview of YM followed by a summary presentation of its segmental and autosegmental phonology. There follows a discussion of the role of tone in YM inflectional and derivational morphology and patterns of tonal allophony that are dependent on phonological and morphosyntactic factors. Section 4 presents patterns of tonal variation related to verbal inflection in the irrealis, incompletive, completive and negative irrealis. We examine both tonal marking and segmental alternations. This study ends with a comparison of YM with verbal inflection in closely related Xochapan Mixtec to suggest the possibility of a regional pattern that typifies Guerrero Mixtec.