Addiction is a subject which straddles public and personal interests; societal and criminal justice concerns; and family, social, and medical responses. It is a continuing area of uncertainty and concern for society and professionals trained in the field. This Very Short Introduction presents the basic facts about addiction: what it is, how and why it develops, how it is treated, and how society can respond to it. Addictions to both illicit drugs and licit drugs (e.g., alcohol) are covered, as is the possibility that certain behaviors not involving drug use (e.g., compulsive gambling) can qualify as addictions. Keith Humphreys provides a jargon-free account of our present understanding of addiction, from treatment evaluations to studies on the effects of public policies. He also illuminates the personal experience of addiction and recovery. Humphreys considers why some people become addicted and others do not, what treatments exist to help people who are addicted, and how the laws and regulations society establishes about drugs affects the rate and experience of addiction.