Security is now and has always been the primary function of government. All societies require some form of law enforcement capability to function effectively. Throughout history, governments of all types have relied on either public police agencies or informal means to effect conformity to social norms, standards, and laws. Given how essential law enforcement is to society, it is surprising how little we really know about how it actually functions. The job of law enforcement is always complex and sometimes dangerous. Police function under much public scrutiny, yet the complexities of what police do and why they do it rarely come to our attention. Readers of this encyclopedia will be introduced to the vagaries.