It is widely established that certain psychoactive substances (e.g., alcohol, cocaine) affect brain reward pathways including dopamine, opioid, and glutamatergic neurochemical systems (Kalivas & Volkow, 2005). These biological effects are linked to addiction in some individuals including unsuccessful attempts to reduce intake, narrowing of interests, risky use (continued use despite knowledge of damaging consequences), and physiologic effects (tolerance and withdrawal; American Psychiatric Association, 2013). This special issue recognizes that certain classes of behaviour exert strong influences over these reward pathways and thus are prone to repetition, that is, constitute “behavioural addictions.”