Three studies showed that information used in determining a target memory’s source may be derived not only from the target event itself, but also from other nontarget events or memories. Subjects were more likely to claim that an imagined object was perceived when it physically resembled or was conceptually related to another specific item that was actually perceived, relative to when there was no physical resemblance or semantic relation. Furthermore, error rates for imagined items increased with the number of perceived items that they resembled. However, subjects’ orienting task at encoding (perceptually biased or perceptually plus conceptually biased) did not systematically affect error rates. The results indicate that reality monitoring decisions about a target object are influenced by similar physical and conceptual information that was derived from other objects.