This chapter describes the root-word method for organizing the documentation and teaching and learning of polysynthetic languages. The root-word method’s foundations are in applied linguistics. It is a simplified, grammar-based approach to organizing the structures of polysynthetic languages that makes exponential acquisition possible. Root-word method second language acquisition processes focus on the sequential and scaffolded acquisition of the structures of a polysynthetic language in an order from simple to increasingly complex through a structural-functional root-word method syllabus delivered to learners through interactionist approaches to second language acquisition in full-immersion instructional frameworks. This chapter also describes how the Onkwawén:na Kentyókhwa Adult Mohawk Language Immersion Program has used the root-word method to create highly proficient second-language speakers and users of Kanyen’kéha (Mohawk) since 1998 at Ohsweken, Ontario, Canada, who are now re-establishing the intergenerational transmission and normalization of Kanyen’kéha.