Private security has become a pervasive feature of modern North American policing, both because of its rapid growth since 1960 and because it has invaded the traditional domain of the public police. Because this development has been viewed as an addendum to the criminal justice system, its significance for social control has not been recognized. This paper traces the development of private security in Canada and the United States since 1960, examines the reasons for its present pervasiveness, and explores its essential features: it is non-specialized, victim-oriented, and relies on organizational resources as sanctions. We conclude that private security is having a major impact on the nature of social control.