Defining the boundaries of private security, like defining the boundaries of policing, raises complex conceptual issues upon which several writers have commented (see, for example, South 1988). Though I shall discuss some of these conceptual issues later, the approach taken here, being primarily a descriptive one, enables me to present a broad review of the industry in a single chapter. It should be borne in mind, however, that statistical data on the industry are notoriously unreliable, particularly in the light of conceptual debates about where the precise boundaries of the sector should be drawn. For that reason, the data presented in this chapter should be seen less as objective facts, than as broad indications of general trends.