This book provides the first reconstruction of Proto Minjim, the ancestor to six Trans New Guinea languages spoken in Madang Province, Papua New Guinea. It discusses several interesting problems in the reconstruction, such as the development of a system vowel intrusion in complex consonant clusters, and several innovations to the pronominal system. The book also focuses on the particularly high rates of irregular sound change in the history of the Minjim languages, and develops a theoretical and methodological framework for approaching that data. Finally, it proposes 257 lexical reconstructions to Proto Minjim, and an additional 157 to Proto Lower Minjim.