With millions of people becoming multilingual writers in the globalized digital world, this book helps to empower writers to connect with their readers and project their identities effectively across languages, social contexts, and genres. In a series of closely-related studies that build on each other, we look comprehensively at how writers develop their ability to construct meaning for different audiences in multiple languages. This book, which draws on various approaches (including a social view of writing, multicompetence, adaptive transfer, complex systems theory, motivation, and translanguaging), contributes to on-going efforts to integrate differing approaches to multilingual writing research. This book focusses on how writer agency (control over text construction), audience awareness (ability to meet expectations of prospective readers), and writer identity (projection of image of the writer in the text) progress as multilingual writers gain more experience across languages. The within-writer, cross-sectional text analysis (Chapters 2-5) examines 185 essays written in Japanese and English by eight groups of writers from novice to advanced (N=103), supplemented by insights from these writers reflections. We explore how they employ three kinds of text features (discourse types, metadiscourse, and self-representation), which relate to their developing agency, audience, and writer identity in their text construction, and propose a new model for writer voice construction based on those features. The four case studies (Chapters 6-9) focus on five university students and six professionals to examine closely how individual writers agency, audience, and identity are interrelated in their text construction in two or three languages and diverse genres, including academic and creative writing. The combined studies provide new insights into multilingual writing development by revealing the close interrelationship among these three principal aspects of writing across languages. They also demonstrate the writers multi-directional use of dynamic transfer (reuse and reshaping) for L1, L2, and L3 text construction, and the use of mixed languages L1/L2 or L1/L3 (translanguaging) for composing processes, in addition to the creative power of multilingual writers. One significant contribution of this book is to provide models of innovative ways to analyze text and new directions for writing research that go beyond complexity, accuracy, and fluency. Categories and detailed examples of text features used for writer voice construction (e.g., specific characteristics of Personal, Emergent, and Mature Voice) are helpful for writing teachers and for developing writers to improve ways of conveying their own intended writer identity to the reader. The studies break new ground by extending our analysis of L2 writing to the same writers L1 and L3 writing and multiple genres.