This book explores a remarkable parallelism in American literary and legal histories: the parallel between naturalism and naturalization. At the turn of the twentieth century, with the influx of unprecedented waves of immigration, the judiciary is at a loss to define who is "white" and who is not. In the courts of law, "whiteness" becomes a performance of cultural assimilability rather than a biological fact. It is this same cultural code of whiteness, this book argues, around which the literature of naturalism revolves by engaging in naturalization debate of its own.