Most Circular Economy (CE) research to date has focused on supply-side factors such as the design, implementation, and monitoring of Circular business models, with comparatively little attention given to the role consumers and consumer psychology are likely to play in CE transition. A key driver of the CE framework is widespread public engagement in non-ownership or "access-based" consumption. In the absence of legally established property rights, the extent to which consumers experience a subjective sense of ownership over accessed (i.e., rented or shared) goods and services will be important in both understanding and fostering CE development. This paper introduces the construct and theory of psychological ownership (PO), discussing empirical evidence for its role in access-based consumption, primarily consumers' use of product-service systems (PSSs). Overall, there is reasonable evidence that PSS users can and do develop a sense of psychological ownership for rented items with, by implication, accessed goods and services activating at least one behavioural pathway or "route" to its development. Once attained, PO tends to have a positive-often mediating-impact on users' perceptions, attitudes, intentions, and behaviour towards rented product-services, with stronger PO having greater influence. A conceptual application of Psychological Ownership Theory to access-based consumption-hence the Circular Economic framework-is forwarded, with potential frustrations to PO development, plus implications for marketers and CE strategists, also discussed. With relevant literature, still sparse various directions for future research are also suggested.