Spanish in the Southwest region of the United States predates the appearance of English in this country. The language has had an uninterrupted presence in the Río Grande corridor since 1598, and has spread geographically and demographically over the last four centuries. Despite that growth, it is being lost among younger generations that trend toward English monolingualism; thus, Spanish exists in a tremendous state of flux in the U.S. Southwest. The present volume´s principal goal is to provide a window into this dynamic through a collection of essays focused on linguistic and sociolinguistic topics on Southwest Spanish. It includes studies of its history, its maintenance and the shift to English, descriptive studies of current varieties of the language, issues in attitudes and identities of its speakers, and language politics and policies in Spanish Heritage Speaker pedagogy. In doing so, this book seeks to capture a historic moment in the constantly unfolding linguistic and political realities that both encourage and threaten the existence of Southwest Spanish.