Defense attorneys in drug cases are increasingly inquiring into the reliability of procedures used by the State for identifying the drugs at issue. This may involve inquiring into the basis for a chemist's opinion about a drug's identity, the chemist's qualifications, or the type of analyses performed. A part of this trend in the defense of drug cases is the rapid rise of the "species defense," which attacks a questionable legal definition of marijuana that has remained unchallenged for over 30 years. This trend has implications for the police officer. If the identity of the substance at issue is being challenged, the chain of custody of the drug evidence becomes crucial. Also, the officer may be called upon to offer expert testimony to identify the substance as a drug. Although such testimony is most often presented on the issue of "probable cause" for making an arrest or a search, expert testimony might also be elicited from the arresting officer at trial. Examples of when the officer's experience and expertise are used to provide the identity of the substance itself are offered in this chapter. Drug identity issues in the drug testing of employees are discussed as well.