This chapter offers a primarily philosophical account of addiction. It examines addiction from conceptual, phenomenological, and ethical perspectives. Addiction is characterised as a persistent engagement in ‘fixing’ or ‘soothing’ or ‘self-medicating’ behaviour, which persists despite negative consequences. Addiction is complex: its signs and symptoms may not be obvious (especially early on); its causes and conditions are even less obvious; and in some cases it may initially help, not hinder, the athlete in achieving their goals Addictive behaviour raises important questions about free will and moral responsibility. The chapter examines attitudes towards active addiction in sport and argues for a more consistent and enlightened approach to addiction in relation to athlete welfare practices and attitudes.