The law regulates addiction in two primary ways: by limiting access to controlled substances and by criminal and civil law doctrines pertaining to addicts. This chapter first addresses the basic definitional and conceptual issues concerning addiction. Then it turns to the justification of substance regulation in the USA and public policy issues. It suggests that the right to use substances recreationally, even at the risk of negative consequences such as addiction, is weighty and that regulation of substances and addiction-related behavior by criminal law is problematic. Next, it considers whether addiction should be a mitigating or excusing condition for crime and whether addicts can be involuntarily civilly committed. It describes the current state of the law and proposes that, in most cases, addiction should not excuse criminal offending and addicts should not be civilly committed. A final section considers social and criminal justice policies that could alleviate the costs of addiction.