This chapter situates the historical policing of suspicious behaviour within a conceptual and criminological framework. It explains the idea of proactive policing based on suspicion, demonstrating that an understanding of the historical roots of this concept and the ways in which it has shaped contemporary policing practices provides a new perspective on the challenges currently faced in policing today. The introduction situates the study within three key criminological and sociological frameworks and their historical dimensions. These are: the enduring project of policing urban public order, the deeply rooted practice of policing based on suspicion and its role in shaping deviance, and the concept of the ‘underclass’, or the sections of society perennially targeted by police. These frameworks facilitate a detailed understanding of the embedded nature of targeted proactive policing practices and their contemporary implications. The chapter also explores the wide range of sources used in the study, including the Old Bailey Proceedings, police court reports in newspapers, Parliamentary Select Committee reports, archival sources, guides and instructions for police officers and legislation relating to policing, and sets out the structure of the subsequent chapters.