This dissertation explores the argument-typing system of Blackfoot, a Plains Algonquian language spoken in Southern Alberta and Northwestern Montana. It develops a classification of the phrases, words, and morphemes in Blackfoot that are associated with arguments of the predicate (nominal expressions and argument-indexing verbal morphology) according to their internal and external syntax. The analysis sheds light on how and why Blackfoot displays properties of a non-configurational language. The main thesis is that non-configurationality in Blackfoot is a conspiracy resulting from properties of Blackfoot’s argument-typing system, and in particular the PROXIMATE/OBVIATIVE contrast, a type of reference-tracking morphology that disambiguates between multiple 3rd persons in a clause. The dissertation begins with a discussion of the theoretical assumptions, methodology, and the main proposal (Chapter 1) as well as a background on the relevant properties of Blackfoot morphosyntax (Chapter 2). Following that is a detailed discussion of the internal and external syntax of inflected nouns (Chapter 3), demonstratives (Chapter 4), person prefixes (Chapter 5) and number suffixes (6). Chapter 7 discusses the implications of Blackfoot’s argument-typing system for non-configurationality. Blackfoot is shown to be a partially non-configurational language, in which proximate nominal expressions are not subject to the same distributional constraints as obviative ones (i.e., proximate nominal expressions display non-configurational properties such as free word order and extensive use of null anaphora). Finally, Chapter 8 considers the proximate/obviative contrast in a broader cross-Algonquian context. The data and generalizations presented in this dissertation are largely from the author’s own fieldwork with two native speakers over a ten year period, and these are supplemented with data from text materials glossed and annotated by the author. As such, a key contribution of this research is empirical; it contributes to the documentation and analysis of this endangered First Nations language.