Abstract Quechua language varieties spread northward into parts of Ecuador, Colombia, and Northern Peru, and were adopted as a native language by speakers of earlier Pacific, Highland, and Amazonian languages in a process of language shift. This process started in the fifteenth century with the Inca state, and is still going on in some regions in the Piedemonte, where speakers of smaller languages are acquiring Quechua as a second, and their ultimately primary language. These Quechua varieties underwent numerous changes which this chapter investigates from the perspective of substrate influence, building on knowledge gathered in creole studies. The chapter further discusses the extent to which substrate influence is relevant to all Northern Quechua varieties or only a subset thereof.