It is the intention of this thesis to effectively describe what is known about EI systems to date. Many sources of information are used, beginning with peer reviewed journals such as Justice Quarterly, Police Quarterly, Policing: An International Journal of Police Strategies & Management, Police and Society and The American Journal of Criminal Justice. Also reports from criminal justice research affiliates will be used like the National Institute of Justice and the National Criminal Justice Reference Service. This thesis will work towards creating a comprehensive outline of the history of EI and future possibilities. With the aid of extant research, inquiries into the effectiveness of various EI systems, their shortcomings, or even best practices will be addressed. The aim is to review the existing discussion essentially paving the way for future researchers to conduct primary research studies on EI effectiveness. By accumulating, and subsequently compiling available research, the hope is to identify key arguments and perspectives on these systems and their implementation.