In 2011, an estimated 22.5 million Americans ages 12 or older were current (past month) illicit drug users, meaning they had used an illicit drug during the month prior to the survey interview; this represents 8.7 percent of the population aged 12 or older. Illicit drugs included in the survey were marijuana/hashish, cocaine (including crack), heroin, hallucinogens, inhalants, or prescription-type psychotherapeutics used nonmedically. Data are reported for the use of each of these drugs. Marijuana was the most commonly used illicit drug. Slightly more than half (51.8 percent) of Americans ages 12 or older reported being current drinkers of alcohol, similar to the rate in 2010 (51.8 percent). The rate of current alcohol use among youths ages 12-17 was 13.3 percent. Past-month binge and heavy drinking rates among underage persons declined between 2002 and 2011. In 2011, an estimated 68.2 million Americans ages 12 or older were current (past month) users of a tobacco product, 26.5 percent of the population in that age range. Data are also presented on the initiation of substance use (incidence or first-time use) within the past 12 months; prevention-related measures for youth; and substance dependence, abuse, and treatment. Extensive tables and figures and appended survey methodology, statistical methods and measurement, other sources of data, and 56 references