This is a reconstruction of Proto-Ersuic, the ancestor language of Lizu, Tosu, and Ersu, three closely related languages spoken in southwestern Sichuan which are generally considered to be part of the Qiangic branch of Tibeto-Burman. Approximately 800 lexical items are reconstructed based primarily on data from six sources: Mianning Lizu (data collected by the author in Mianning County, Sichuan, in 2008 and 2010), two sources for Kala Lizu (Muli County, one modern and one older source), Naiqu Lizu (Jiulong County), and two varieties of Ersu (Zeluo and Qingshui, both in Ganluo County).

Chapters 3 and 4 lay out the complete inventory of Proto-Ersuic initials and rhymes, supported by cognate sets demonstrating regular sound correspondences, with exceptions carefully noted.

Chapter 5 offers a tentative reconstruction of the lexical tones of Proto-Ersuic.

Chapter 6 presents an outline of shared morphosyntax that can be reconstructed to the Proto-Ersuic level.

Chapter 7 brings together all the sound changes implicit or explicit in Chapters 3 and 4, organizing them by language, and ordering them chronologically. From these sound changes emerges a picture of the internal structure (i.e. subgrouping) of Ersuic.

Chapter 8 takes a top-down approach, examining the sound changes from Proto-Tibeto-Burman to Proto-Ersuic and attempting to find regular patterns in the development of Proto-Tibeto-Burman rhymes, initials, and prefixes.

The final chapter (Chapter 9) addresses the place of Proto-Ersuic in Tibeto-Burman.