The scientific field of language acquisition research examines a basic foundation of the human experience: How children come to speak their first language. For decades the field has largely focused on languages with millions (or even billions) of speakers, such as Spanish, French, Japanese, and English. We know very little about how children learn to speak most of the other 7000 languages around the world. Approximately half of these languages are in danger of disappearing, which includes all of the Algonquian language family, one of the largest groups of indigenous languages in North America. Algonquian languages such as Northern East Cree (NEC) are radically different from those typically studied in language acquisition research, and as these languages cease to be spoken, we lose the chance to understand how children acquire the fundamentally human capacity of linguistic expression. This dissertation project explores how children learn to speak NEC, one of the few remaining indigenous languages in North America still learned by children as a first language. This project analyzes and improves video/audio recordings collected by the Chisasibi Child Language Acquisition Study (CCLAS), and this dissertation also includes new fieldwork with adult speakers of NEC to provide more insight into how the language works and the stages children go through when learning the language. This dissertation project offers a range of benefits for science and for communities. It will enhance existing documentation of NEC and include child speech as well as speech from adults to children, both of which are underrepresented genres in language documentation. It will also expand the purview and deepen the diversity of language acquisition research. Furthermore, this dissertation can help provide Cree communities with better tools for language assessment and speech-language pathology, so that children may have better support on their journey to become speakers of their language. Lastly, the documentation and description generated by this dissertation can help inform the development of curricula and teaching materials for learners of the Cree language.<br/><br/>This dissertation will enhance and expand the documentary record of NEC. This project will create new language documentation as well as enrich existing recordings of child and child-directed speech collected by the Chisasibi Child Language Acquisition Study (CCLAS). The focus of this dissertation is the first language acquisition of the expression of possession, which is a fundamental concept in cognitive and linguistic development. This project will create and advance language documentation on two fronts. First, research involves working with adult speakers of NEC to review CCLAS recordings and elicit and transcribe adult-like targets. This will produce hours of transcribed and annotated audio recordings of NEC as well as unique metalinguistic commentary and analysis. Second, these adult targets, transcriptions, elicitations, analysis, commentary, and notes will be used to enrich the existing CCLAS corpus. This work will help enable CCLAS to make additional transcripts, annotations, and media files publicly available. Through this work, this dissertation will help break new scientific ground. For example, this dissertation examines speech genres often absent in language documentation, and it enriches the range and typological diversity of language acquisition research. This project can also provide insight to help ensure that methods and tools in language assessment and speech-language pathology are linguistically and culturally inappropriate. The findings from this research can also inform the creation of curriculum and pedagogical materials to benefit not only second language learners but also meet the needs of schools teaching Cree-speaking children about the structure of their mother tongue.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.