Eunuchs occupied a prominent position within the Byzantine Empire, particularly from the fourth century onwards. Their pervasive presence, especially within the imperial court and the political, military, and religious spheres, rendered them significant to Byzantine society. This book aims to offer a new perspective on the history of eunuchs in Byzantium by undertaking a close examination of Byzantine legal sources that have received limited attention in previous scholarship. The analysis centres on legislation promulgated between the reign of Justinian I (527–65) and the end of the Macedonian dynasty (1056)—a period marked by both the heightened visibility of eunuchs and significant legislative activity. Focusing on the legal framework, the study investigates how emperors and their governments understood the place of eunuchs in society and addressed issues related to eunuchs through legislative activities. This introductory chapter outlines the scope and objectives of the book. It discusses the research background, methodology, and primary sources and offers a concise overview of eunuchs (e.g. their causes, origins, terminology, and definitions).