Teotitlán del Valle Zapotec is spoken in the community of Teotitlán del Valle, in the Central Valley of Oaxaca in the Mexican state of Oaxaca. Teotitlán Zapotec is one of the Central Zapotec languages, which belong to the Zapotecan language family within the Otomanguean language stock. Teotitlán Zapotec has two mid-front vowels, [ε] and [e]. The distribution of these two mid-front vowels is conditioned by the nature of the adjacent consonants and accent and presents challenges to formal analysis due to a number of properties predictive of the distribution: the disjunctive set of consonants conditioning the alternation, the ganging effect of consonant type and syllable structure as triggers, the featural characterization of the process as raising assimilation, and asymmetries between derived and non-derived environments in the observed patterns.