||This dissertation is a comparative grammar of the four known Xinkan languages of southeastern Guatemala (Guazacapán, Chiquimulilla, Jumaytepeque, and Yupiltepeque). The goal of this grammar is twofold: to provide a thorough description of the Xinkan languages and to reconstruct Proto-Xinkan from which these four languages developed. Xinkan languages currently are represented by only three people, all of whom are second language users of the language. This grammar begins with an introduction to the language family, the past research on Xinkan languages, and the goals behind the descriptions. In addition to this introduction to the language, a typological overview is included which highlights and outlines the interesting typological phenonmena in the languages with specific references to sections within the grammar for a detailed analysis of each part of the language.