This work is a comprehensive description of the grammar of Sierra Popoluca, a Mixe-Zoquean language spoken by approximately 28,000 people in Veracruz, Mexico. This detailed description and analysis includes an overview of the language and its family, its typological features and its phonology. The grammar also provides an overview of the word classes, including verbs, nouns, relational nouns/postpositions, adjectives, adverbs, 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. An agglutinating, polysynthetic, head-marking language with ergative-absolutive alignment and sensitivity to animacy and saliency hierarchies, Sierra Popoluca has a number of strategies to form complex predicates, which include verb serialization, noun incorporation, and dependent verb constructions. These complex predicate formation strategies and sentence-level syntax are also described here. A compilation of interlinearized texts appears in the appendix. There is no competing work that provides the breadth and depth of coverage of the Sierra Popoluca grammar.