The document provides an overview of the history of policing in America from the colonial era to the present. It discusses the origins of policing from English institutions like the constable and sheriff, and how the first modern police departments emerged in the 19th century in response to urbanization and immigration. It then outlines three major eras in American policing history - the political era from 1830s-1900, the professional era from 1900-1960s, and the era of conflicting pressures from 1960s onward. Key reforms and developments that changed the role of police are also summarized.