This book explores the internal structure of personal pronouns in Brazilian Portuguese, with a special emphasis on the first-person singular, which exhibits severe syncretism in this language. This study is an investigation into the formative features of pronouns in Brazilian Portuguese and their relationship with the phenomenon of syncretism. Empirically, this book provides a description of the internal structure of personal pronouns in Brazilian Portuguese, showing that the traditional phi-features used to construct a pronoun (person, number, gender, and case) are actually categories which encompass more elemental features which define the content and the shape of a pronoun. It shows that more elementary component structures of the person, number, gender and case categories are able to satisfactorily describe the pronoun system in Brazilian Portuguese, meaning that different pronouns (and their syntactic roles) may be described based on their inner composition. In terms of theory, this book defines which elementary formative features form a pronoun, how these features are composed, and what the syntactic consequences are.