Clinicians encounter patients with substance use disorders in all clinical settings. In 1995, health care spending in the United States associated with alcohol, tobacco, and drug abuse was estimated to be more than $114 billion (Horgan et al. 2001). It has been estimated that there were nearly 2 million drug-related emergency room admissions in 2004, and that out of those, approximately 1.3 million were associated with drug use or misuse (SAMHSA 2006). As much as 40% of medical inpatient admissions are related to the complications of alcohol dependence (Horgan 1993), and on any given day more than 900,000 individuals receive alcohol or drug treatment in specialized treatment programs, with most of these receiving treatment as outpatients (Horgan et al. 2001). There were nearly 1.7 million admissions to publicly funded substance abuse treatment programs in 2003 (SAMHSA 2006). However, despite the prevalence of these disorders in both general and treatment-seeking populations, substance use disorders are often undetected and undiagnosed in a variety of clinical settings (Cummings and Cummings 2000; Deitz et al. 1994) and fewer than one-third of physicians in the United States carefully screen for addiction (National Center on Addiction and Substance Abuse 2000). A thorough and accurate substance use history should therefore be a part of any medical or psychiatric interview.