This chapter focuses on conceptual (as opposed to theoretical) developments in psychology and inquiries into the criteria by which such developments constitute progress. The chapter distinguishes between the issue of (a) what are units of psychological analysis and (b) what are objects of psychological research, positing that the units of analysis are human (and animal) individuals and that the objects of research are (cognitive, behavioural, and experiential) capacities, which are often individuated by means of folk-psychological terms. While this suggests that conceptual progress occurs when concepts provide improved descriptions of the objects in their extension, the chapter raises some doubts regarding the (seemingly intuitive) notion that are natural and/or ahistorical facts of the matter that settle what psychological concepts ‘really’ refer to. It concludes by arguing that (1) conceptual progress occurs when concepts track their (potentially changing) objects and (2) such efforts rely on the availability of epistemic resources, which include both propositional and non-propositional knowledge. Regarding this latter point, the chapter articulates a broad conception of progress in psychology as the accumulation of epistemic resources and argues that the history of psychology provides us with a trove of such resources.