The manual consists of three chapters: Behaving Systems, Impairing Drugs, and Investigative Process. The first chapter, Behaving Systems, focuses on explaining how the central nervous system (CNS) is organized and how it functions, as well as how alcohol and/or drugs impair its functioning. The elements of the CNS, including the brain, the spinal cord, and associated structures, are described, followed by a discussion of human intellect and reasoning, which is tied to the coordinated movement of the CNS. The second chapter, Impairing Drugs, focuses on the effects of various substances on the CNS. This chapter includes a description of Pharmacology and Toxicology, as well as detailed descriptions of how numerous drugs act upon the CNS and the physical and cognitive characteristics pointing toward drug intoxication. The most useful detection techniques for each type of drug are enumerated in addition to a plethora of other information about how the body metabolizes each of the drugs, how they affect individuals, and any outward signs of drug ingestion that would signal the need for further evaluation by an officer. The third chapter focuses on the investigative process, offering information on the elements of the offense and the driving patterns of impaired drivers. This chapter also includes information on how to identify a possibly impaired driver, such as through the use of observation and divided attention questioning employing multiple requests, rapid follow-up questions, and unusual questions. Standardized field sobriety testing is described, including procedure descriptions for the One-Leg Stand, the Walk and Turn Test, and the Finger Count Test, among many others. Information on evidence collection and admissibility, report writing, court testimony, and case law close this manual on advanced DUI investigation training. Index