More than thirty years of research has examined “theory of mind” in non-human animals, human infants, children and adults, and human brains. This work has led to many insights, but, if anything, the object of study has become less clear as the weight of evidence has increased. By turns, researchers conceptualise “theory of mind” as a set of concepts, a collection of cognitive processes, and an individual difference variable. I shall argue that these conceptions all have their virtues, but that it is unhelpful to confound them and probably unwise to try to investigate them all with the same narrow set of experimental tasks. Newly-emerging methods have great potential for advancing our understanding of “theory of mind”, all the more so if we refine our ideas about what we are studying, and why.