Chicahuaxtla Triqui (Otomanguean, Mexico) is one of the rare tone languages with five contrastive level tones and its underlying tone system is even more complicated than its surface five-level tone system. The complexity of its underlying tone system has developed through the historical tone shifts from Proto-Triqui. The surface tone system of Chicahuaxtla Triqui is also unusually complicated and its complexity led to the insufficient analysis of the previous studies (e.g. Longacre 1952, 1957, 1959; Good 1978). To understand the tone system and tonal phonology of Chicahuaxtla Triqui, we must know their diachronic development from Proto-Triqui because historical tone shifts, which happened in Chicahuaxtla Triqui, added more complexity to the original tone system and tonal phonology of Proto-Triqui. In this dissertation, I clearly distinguish and define underlying tones and surface tones in Chicahuaxtla Triqui to avoid unnecessary confusion first. Then, I explain how Chicahuaxtla Triqui tones have historically changed from the original Proto-Triqui tones. Finally, I describe all identified tonal phonology of Chicahuaxtla Triqui (e.g. potential tone patterns, possessive tone patterns, tone alteration patterns with clitic pronouns, tone alteration patterns in tone sandhi environments) based on my fieldwork data and explain its underlying phonological structure through diachronic analysis. I almost always compare Chicahuaxtla Triqui with other Triqui languages (Itunyoso Triqui, Copala Triqui) in this dissertation because comparative and historical linguistic analysis is crucial to understand the tonal phonology of Chicahuaxtla Triqui. This is the first comprehensive comparative and historical linguistic study of Triqui languages and many open questions in Triqui languages are solved through comparative and historical linguistic analysis in this dissertation. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]