This dissertation is a comprehensive description of the grammar of Sierra Popoluca (SP, aka Soteapanec), a Mixe-Zoquean language spoken by approximately 28,000 people in Veracruz, Mexico. This grammar begins with an introduction to the language, its language family, a typological overview of the language, a brief history of my fieldwork, and the methodology undertaken in this study. The grammar continues with a description of the phonology of SP, followed by an overview of the word classes, including verbs, nouns, relational nouns/postpositions, adjectives, adverbs, and numbers, and formative types. The bulk of this grammar is devoted to the morphosyntax of Sierra Popoluca, including nouns and nominal morphology, verbs and verbal morphology, and the mechanisms for expressing tense, aspect, mood, and modality. The grammar also describes the complex predicate formation strategies and sentence-level syntax. A compilation of interlinearized texts appears in the appendix.