In the sustainability transitions literature, social phenomena have mostly been examined in relation to - and at the level of - collective forms of action. Here our focus is on psychological, primarily individualistic approaches to understanding action as behaviour, with particular attention to consumption and technology acceptance. We document and discuss the ways in which the psychology of agents or actors has been described and theorised in these contexts within the sociotechnical transitions literature to date, both implicitly and explicitly. A review of the latter literature shows that while actor motivation and behaviour are often implicitly referred to, these are rarely theorised explicitly using psychological concepts. Reasons for the limited use of individual-level, psychological constructs are discussed and suggestions for how these may be more closely connected to structural and collective processes are made.