This chapter outlines the scope of the problem of heroin addiction, history of its discovery and its pharmacological properties, based on which description of various clinical aspects of heroin use and addiction are presented and their immediate and remote sequelae are described. Special attention is paid to the description of individual-level harms associated with heroin use and their clinical management. Global socioeconomic aspects of heroin addiction are discussed as well as the current and past incentives to reduce heroin production, trafficking and use.