This all inclusive reference book deals with all aspects of DUI/DWI and is aimed exclusively towards the investigation of driving under the influence of alcohol and/or drugs. It addresses the subject matter thoroughly and is geared toward the experienced police officer actively involved in DUI/DWI detection and arrest. The book can be carried in a patrol car as a ready reference or be used in the classroom. All of the necessary information needed to professionally investigate incidents of impaired driving, prepare a comprehensive report and then be able to testify as an expert in a court of law is provided. It goes into detail in explaining the intricacies of why a person becomes intoxicated, why the Horizontal Gaze Nystagmus Field Test is a valuable and valid psycho-motor or field test, and it also provides a step by step approach to extrapolating blood alcohol content. The central nervous system of the human being is explained in a manner that is easily understood by the average person, connecting the how and why the CNS is affected and therefore how this impairment manifests itself as a drunk driver as opposed to a drunk pedestrian. The manual also contains sections dealing with alcohol, depressant and stimulant drugs, which are critical to the proper understanding of the observable effects of drugs and alcohol. Also included are instructional objectives for each section, section quizzes and a comprehensive final exam. It will not only help to increase the confidence level of those everyday working street cops who must make decisions about whether to arrest or not arrest on any given impaired or intoxicated driver situation, but it will also provide the basis for the street cop to excel in this field of law enforcement and prepare themselves as an expert in the detection and arrest of DUI drivers.