This national report summarizes findings from the 2015 National Survey on Drug Use and Health (NSDUH) on trends in the behavioral health of people aged 12 years old or older in the civilian, noninstitutionalized population of the United States. It details the rates and numbers of use of illicit drugs (e.g., marijuana, cocaine, heroin, hallucinogens, inhalants, and misuse of prescription-type pain relievers, tranquilizers, stimulants, and sedatives), alcohol, and tobacco products; rates and number of substance use disorders (SUDs); and rates and numbers of persons with any mental illness (AMI), serious mental illness (SMI), and major depressive episode (MDE). Results are provided by age subgroups. Substance use trends are presented for 2002 to 2015, while trends for most mental health issues are reported for 2008 to 2015. Other topics included in the 2015 NSDUH are being published separately as data reviews. These data reviews cover national trends in suicidal thoughts and behavior among adults, substance use treatment, mental health service use, initiation of substance use, and substance use risk and protective factors.