Drugs are referred to by several different names, including controlled substances and narcotics. Strictly speaking, narcotics are only one category of drugs when the principle pharmacological effect is used as the classification scheme. However, in law enforcement, many agencies refer to their specialized unit as narcotics. Controlled substance is the nomenclature that arose out of the Comprehensive Controlled Substances Act of 1970 (CSA), a landmark law in the long running efforts to regulate drugs, their distribution and use, which introduced the term “controlled substances” as the accepted way of referring to these materials. With many years of disjointed approaches, the CSA was regarded as the definitive means of classifying drugs, also providing storage and sentencing guidelines, though it must be noted that tobacco and alcohol are excluded from the CSA. Classification by the CSA is into one of five schedules based upon accepted medical use in the United States and the potential for abuse, with Schedule I containing those drugs without currently accepted medical uses and a high potential for abuse, such as heroin. Since 1970, however, there has been a rapid and ever-evolving increase in the number of “designer drugs” produced in clandestine laboratories. They require additional legislation for both the final product and the precursors used in their manufacture. Further, more recent changes in public attitude have led to the decriminalization of marijuana in many states. With confusing nomenclature, for the remainder of this chapter, the term “drugs” will be used to cover this particular category of illicit substance evidence.