The Inquisition has long stood as one of history's most emblematic instruments of fear—a system that claimed to defend faith while policing thought. Yet behind the image of dungeon and pyre lay something more complex: an institution that served as the administrative arm of both church and state, where theology became an instrument of governance. This book explores the Inquisition not as isolated cruelty but as a structured mechanism of control, deeply embedded in the evolution of European power. Through papal decrees, inquisitorial manuals, and trial records from Spain, Italy, and the Holy Roman Empire, it reveals how questioning belief became synonymous with challenging authority. Heresy, witchcraft, and conversion were less matters of doctrine than tools of surveillance and conformity in societies struggling to define orthodoxy amid political change. Drawing on recent archival research and comparative studies, the narrative connects medieval heresy trials to Enlightenment censorship—and to modern systems of ideological policing. The Inquisition's legacy endures less in religion than in how societies learn to justify control in the name of truth.