Public law enforcement agencies differ from private security agencies in two important ways: (1) law enforcement employers, as public agencies, have more legal authority; and (2) law enforcement personnel encounter more legal restrictions. In addition, public law enforcement personnel are protected from civil liability for false arrest when they have probable cause that a crime was committed. Private security personnel, on the other hand, must be certain that a crime was committed if they make an arrest; otherwise, they are liable if there was no crime. Traditionally, law enforcement agencies have not realized the importance of developing a cooperative relationship with private police and security agencies. Although some conflict still exists between law enforcement and private security, there has been considerable movement toward cooperation. Law enforcement agencies should recognize that many of their activities are performed by private security agencies, for example, in colleges, hospitals, shopping malls, housing projects, and individual residences. 26 references, 1 table.