Ian Hacking’s theory of ecological niches offers a comprehensive framework to account for the transformation of mental health issues in societies, bridging key theoretical perspectives such as neo-Marxism, interactionism, constructivism, and poststructuralism. This chapter illustrates this through the case of ‘behavioural addictions’, reflecting on how, since the 1970s, these ‘new’ pathologies have proliferated in the West. Activities traditionally encouraged when practised with moderation—working, exercising, or engaging in sexual activity—are increasingly redefined as addictive when their frequency, significance, or impact exceeds certain normative limits. After presenting Hacking’s ‘historical ontology’, the chapter draws on a multi-sited study of addictions to sex, exercise, and work in Australia and North America to apply the theory of ecological niches and its four vectors reformulated as: category production; observation networks; representational landscapes; and release. The analysis shows that the convergence of these vectors helps understanding the generative processes through which behavioural addictions come to emerge, exist socially and generate meaning in contemporary, global societies.