This chapter reviews the interaction between criminal behavior and substance use. It discusses legal guidelines and precedents in the courts. The chapter provides an overview of assessment tests, tools, and techniques that can be applied to evaluate substance use. There are legally two general issues in the relationship between criminal behavior and substance use. One relates to the possession, sale, and use of illegal drugs as criminal behavior and the other concerns with antisocial behavior resulting from the effect of drug. The majority of arrests for the offense of drug abuse violations are for possession of marijuana. Alcohol and other drugs have been addressed in innumerable cases in both civil and criminal law. Two landmark cases underlie current legal thinking on criminal responsibility and alcoholism and drug addiction. Many measures of substance use are based on the Diagnostic and Statistical Manual of Mental Disorders. The most commonly employed method of assessment used in alcohol treatment agencies to diagnose substance use disorders is the clinical interview. The chapter concludes with a briefly discussion on the literature on the treatment of individuals with a substance use disorder.